Electrospray Ionization Efficiency Scale of Organic Compounds. Talk ...
Transcript of Electrospray Ionization Efficiency Scale of Organic Compounds. Talk ...
1
Electrospray IonizationEfficiency Scale of Organic
CompoundsIvo Leito Merit Oss Anneli Kruve Koit Herodes
University of TartuInstitute of Chemistry
Estonia
ivoleitoutee
14th Nordic MS Conference Uppsala Aug 18-20 2010
2
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
2
3
ESI Ionization
bull The most widely applied ionizationmethod in MS
bull Ionization viabull Protonationbull Deprotonationbull Adduct formation
bull Complex mechanismbull Ion Evaporation Model (IEM)bull Charged Residue Model (CRM)
4
ESI in action (Positive ions)
Image by K K Murray (via Wikipedia)
Positivelychargeddroplets
3
5
ESI mechanism according to IEM
B SH++
H-B+
+
Polar slightly acidified solvent egWater-MeCN (+ HCOOH)
S
Dropsurface
Gas phase
H-B+
H-B+
Dropinterior
We assume the IEM model for small
molecules
We study onlyionization by
monoprotonation
6
Efficiency of ion formation in ESI
bull Not all molecules in a droplet are converted to gas-phase ions
bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions
4
7
ESI Ionization Efficiency (IE)bull IE depends on
bull Molecular structurebull Solventbull ESI and MS Conditions
Different molecules have vastlydiffering ionization efficiencies in the
ESI source
Being able to predict ionizationefficiencies of molecules would be
very useful
8
What determines ionization efficiency of a molecule
bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip
Howeverthere is still a long way to go to gain
complete understanding
5
9
How to measurequantifyexpressionization efficiency of a molecule
bull For applying the scientific method to a phenomenon its extent needs to bemeasured
There is currently no generallyaccepted way to measurequantify
ESI IE
10
Goals
bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment
bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions
bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
2
3
ESI Ionization
bull The most widely applied ionizationmethod in MS
bull Ionization viabull Protonationbull Deprotonationbull Adduct formation
bull Complex mechanismbull Ion Evaporation Model (IEM)bull Charged Residue Model (CRM)
4
ESI in action (Positive ions)
Image by K K Murray (via Wikipedia)
Positivelychargeddroplets
3
5
ESI mechanism according to IEM
B SH++
H-B+
+
Polar slightly acidified solvent egWater-MeCN (+ HCOOH)
S
Dropsurface
Gas phase
H-B+
H-B+
Dropinterior
We assume the IEM model for small
molecules
We study onlyionization by
monoprotonation
6
Efficiency of ion formation in ESI
bull Not all molecules in a droplet are converted to gas-phase ions
bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions
4
7
ESI Ionization Efficiency (IE)bull IE depends on
bull Molecular structurebull Solventbull ESI and MS Conditions
Different molecules have vastlydiffering ionization efficiencies in the
ESI source
Being able to predict ionizationefficiencies of molecules would be
very useful
8
What determines ionization efficiency of a molecule
bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip
Howeverthere is still a long way to go to gain
complete understanding
5
9
How to measurequantifyexpressionization efficiency of a molecule
bull For applying the scientific method to a phenomenon its extent needs to bemeasured
There is currently no generallyaccepted way to measurequantify
ESI IE
10
Goals
bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment
bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions
bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
3
5
ESI mechanism according to IEM
B SH++
H-B+
+
Polar slightly acidified solvent egWater-MeCN (+ HCOOH)
S
Dropsurface
Gas phase
H-B+
H-B+
Dropinterior
We assume the IEM model for small
molecules
We study onlyionization by
monoprotonation
6
Efficiency of ion formation in ESI
bull Not all molecules in a droplet are converted to gas-phase ions
bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions
4
7
ESI Ionization Efficiency (IE)bull IE depends on
bull Molecular structurebull Solventbull ESI and MS Conditions
Different molecules have vastlydiffering ionization efficiencies in the
ESI source
Being able to predict ionizationefficiencies of molecules would be
very useful
8
What determines ionization efficiency of a molecule
bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip
Howeverthere is still a long way to go to gain
complete understanding
5
9
How to measurequantifyexpressionization efficiency of a molecule
bull For applying the scientific method to a phenomenon its extent needs to bemeasured
There is currently no generallyaccepted way to measurequantify
ESI IE
10
Goals
bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment
bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions
bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
4
7
ESI Ionization Efficiency (IE)bull IE depends on
bull Molecular structurebull Solventbull ESI and MS Conditions
Different molecules have vastlydiffering ionization efficiencies in the
ESI source
Being able to predict ionizationefficiencies of molecules would be
very useful
8
What determines ionization efficiency of a molecule
bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip
Howeverthere is still a long way to go to gain
complete understanding
5
9
How to measurequantifyexpressionization efficiency of a molecule
bull For applying the scientific method to a phenomenon its extent needs to bemeasured
There is currently no generallyaccepted way to measurequantify
ESI IE
10
Goals
bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment
bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions
bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
5
9
How to measurequantifyexpressionization efficiency of a molecule
bull For applying the scientific method to a phenomenon its extent needs to bemeasured
There is currently no generallyaccepted way to measurequantify
ESI IE
10
Goals
bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment
bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions
bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
6
11
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
12
Defining ionization efficiencybull Fundamental
bull n in the gas phase is very difficult todetermine
molecules) phase-solution()ions phase-gas(
lfundamenta nnIE =
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
7
13
Defining ionization efficiencybull Practical
bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum
bull CB ndash molar concentration of the base B in the mass spectrum
B
BH
CR
IE +=
14
Agilent XCT ion trap MS with ESI Source
Effluent fromHPLC
Nebulizationgas (N2) inlet
Nebulizerneedle
Sprayshield
Capillary
Skimmer
Octopole 1 Octopole 2
Split lens
Ring electrodeDrying gas(heated N2) flow
Lens 1 Lens 2
High energydynode
ElectronmultiplyerEnd capsCapillary
entrance
Capillaryexit
Atmospheric pressure(spray chamber)
Vacuumpartition
38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)
Ion generation Ion transport and focusing Mass analyzer(ion trap)
Detector
End plate
Meshelectrode
Not all ionsreach theentrance
Ion lossesduring iontransport
Responsedepends on
trapping efficiency
Conclusion R does not measure just ESI IE but the efficiency of the whole
system
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
8
15
Dependence of RBH+ on conditions
bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface
and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop
][]E[]BH[
]BH[
EBH
BHBH
QKK
KPfR ++
+
++
+
+
+=
C Enke Anal Chem 1997 69 4885
16
Assumptions (I)
bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface
bull Drop interior is neutral
bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small
compared to the interiorbull RBH+ is proportional to the amount of BH+ on the
drop surface
C Enke Anal Chem 1997 69 4885
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
9
17
Two Compounds simultaneously
bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the
same solution at significantly lower concentrationthan buffer electrolytes
bull then the following holds
]HB[
]HB[
1HB
2HB
HB
HB
2
1
2
1
+
+
+
+
+
+
=R
R
K
K
18
Two Compounds simultaneously
bull Considering that
bull We get
12
21
22
11
BHB
BHB
HBHB
HBHB
CR
CR
K
K
+
+
++
++
=α
α
+
+
+
=HB
1HB
1
1
]HB[C
α+
+
+
=HB
2HB
2
2
]HB[C
α
==)B()B()BB(
2
121 IE
IERIE
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
10
19
Relative Ionization Efficiency of B1 and B2
bull It is more convenient to use logRIE values
bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS
bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak
heights (areas)
12
21
BHB
BHB
2
121 )B(
)B()BB(CR
CR
IEIERIE
+
+
==
I Leito et al Rapid Comm MS 2008 22 379
20
Compound B1 Diphenylaminebull M = 169 N
H
NH2+
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
11
21
Compound B2 Acridinebull M = 179
N
NH+
22
Mixture of B1 and B2
logRIE = -034
20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154
akridiin
180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218
DPhA
170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015
K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348
1700
1800
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
12
23
Assumptions (II)
bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the
range of 1middot10-6 M
bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway
bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+
bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz
ions can be tuned with a parameter target mass
I Leito et al Rapid Comm MS 2008 22 379
24
Advantages of relative measurement
bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control
bull Ion losses cancel to a large extentbull Similar transmission efficiencies
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
13
25
Experimental details
bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250
spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar
as possiblebull Using the Target mass parameter
of the Agilent XCT IT MSbull Other MS parameters at default
values
26
QA of the resultsbull In all pairs parallel measurements were
done with different concentration ratiosusually differing by more than 10x
bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo
bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
14
27
Circular validation
)B()B(log)BB(log
2
121 IE
IERIE =
)BB(log)BB(log)BB(log 231312 RIERIERIE minus=
logRIE(B2B1)
logRIE(B3B2)
logRIE(B3B1)
28
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
15
29
Compounds
bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others
30
Compounds (I)
N
N
N
NH2
N
NH
NO2
NH2NH2
NO2O2N
NH2
NO2
NO2
NH2
F
N NH2
O2N
NH2
Cl
NO2
N
Aliphatic amines Aromatic amines
NH
NH
N
NH2
NH
NH2
NH2
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
16
31
Compounds (II)
NH
NH
NH
N PN
NN
N
F
F
F
PN
NN
NCl
Cl
PN
NN
ClN P N
N
NPN
NN
Phosphazenes
N N
NH
NH2
NH
NH2
Guanidinesamidines
+NN+
N+
N+
N+
Tetraalkylammonium
N
N
N
N
N
32
Compounds (III)
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOPh
COOPhO
O
O
O
O
O
O
O
F
F
F
Carbonyl compounds
NH2
O
OH
O
O
COOMe
COOMe
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
17
33
Compounds (IV)
N
O
ON
Cl
N N N
N
OHN
S NO N
H
O
S
O NH
O
SN
O NH
O
NCl
N
O
NN+
NN+
OthersHeterocycles
N
NH2
SO
O NH2
34
ResultsESI IE Scale
bull 407measurements
with 250compound pairs
bull Only 116 measurements
are indicatedon the scale
No Compound logIE a Directly measured logRIE values
1 2ClPhP2(pyrr) 615
2 tetrahexylammonium 565
3 4CF3PhP1(pyrr) 555
4 25Cl2PhP1(pyrr) 552
5 PhP1(NMe2)3 518
6 tetrabutylammonium 513
7 tetrapropylammonium 497
8 phenyl tetramethylguanidine 486
9 tributylamine 483
10 hexyl-methylimidazolium 466
11 diphenylguanidine 461
12 tripropylamine 456
13 acridine 442
14 246-trimethyl pyridine 390
15 diphenylamine 418
16 diphenyl phthalate 410
17 1-naphthylamine 404
18 DBU 396
19 tetramethylguanidine 389
20 tetraethylammonium 395
21 methiocarb 388
22 triphenylamine 367
23 NN-dimethylaniline 372
24 ethyl-methylimidazolium 368
25 4-fluoro-3-nitroaniline 365
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 3 25
M Oss et al Anal Chem2010 82 2865
For better view of the scalesee poster No 21
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
18
35
ESI IE Scale(contd)
26 26-dimethylpyridine 341
27 dimethyl phthalate 354
28 triethylamine 353
29 3-nitroaniline 352
30 benzylamine 343
31 sulphanilamide 340
32 methomyl 325
33 aldicarb 322
34 piperidine 316
35 benzophenone 325
36 2-methyl pyridine 302
37 aniline 304
38 N-methyl piperidine 301
39 4-nitroaniline 296
40 pyridine 294
41 dimethyl glutarate 288
42 benzamide 274
43 pyrrolidine 270
44 diethylamine 266
45 phenylbenzoate 244
46 2-nitroaniline 244
47 4-chloro-2-nitroaniline 232
48 dimethyl succinate 214
49 tetramethyl ammonium 215
50 guanidine 195
51 trimethylamine 181
52 dimethylmalonate 146
53 2-cyano phenol 125
54 benzoic acid 122
55 24-dinitroaniline 114
56 26-dimethoxy pyridine 112
57 ethylamine 112
58 2-methoxy pyridine 099
59 3-chloro pyridine 100
60 2-chloro pyridine 097
61 ethyl benzoate 053
62 methyl benzoate 0
bull Values assignedby least-squares
minimization
bull Anchored tomethyl benzoate
IE(MB) = 0
M Oss et al Anal Chem2010 82 2865
36
Compd logIE Compd logIE Compd logIE Compd logIE
2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215
Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195
4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181
25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146
PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125
Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122
Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114
PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112
Bu3N 483 4F3NA 365 DMG 288 EtNH2 112
HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099
DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100
Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097
acridine 442 3NA 352 PhB 244 EtB 053
246TMePy 390 BA 343 2NA 244 MB 0
DPhA 418 sulfA 340 4Cl2NA 232
DPhP 410 Methomyl 325 DMS 214
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
19
37
Consistency of the scale
bull s = 030 logRIE units
bull 143 measurements deviate by more than 02 logunits
bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded
cm nnSSsminus
=
38
Reasons of deviationsbull Too different molecular masses of B1 and B2
bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units
bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units
bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE
bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
20
39
Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]
bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes
bull Should be independent
bull Long-term drift of theinstrument
40
Additional processesbull With O-protonating compounds Na+
adductsbull Not taken into account on the assumption that
Na+ adduct formation does not significantlydecrease [B]
bull With many compounds fragmentationbull Taken into account on the assumption that
fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of
BH+
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
21
41
Dimethyl phthalate vs diphenyl phtahalate
O
O
O
OH+
O
O
O
OH
Ph
Ph
+
O
O
O
ONa+
O
O
O +
O
O
O
Ph
+ O
O
O
ONa
Ph
Ph
+
42
Usefulness of the scale
bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances
bull Semiquantitative determinations to be made without the need to calibrate with each analyte
bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the
molecular level
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
22
43
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
44
ESI IE and molecular structurebull Likely to be important
bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface
area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
23
4545181
367
456
483
logIE
353
∆172
∆027
∆089
∆014
M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537
M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006
M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146
M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174
M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061
45N
N
N
∆103N
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
N
4646
000
122
244logIE
053
∆053
∆122
∆069
46
O
O
OH
O
O
O
O
O
M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57
M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol
pKa_H2O = -73GB = 1941 kcalmollogP = -48
M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500
∆191
Part of the parameters have beencomputed using COSMO-RS
See poster No 21
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
24
47
Attempt to predict ESI IE Training setbull Training set of 42 random compounds
bull Scaled and centered parameters
bull Only pKa and logMV statisticallysignificant
bull R2 = 067 s = 086 log units
ssa
s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=
M Oss et al Anal Chem2010 82 2865
48
Attempt to predict ESI IE Test setbull Test set of 20
compoundsbull Differences between
measurement andprediction rangefrom -16 to 11
M Oss et al Anal Chem2010 82 2865
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
25
49
ESI IE and molecular structurebull Certain trends are seen
bull Size mattersbull Hydrophobicity mattersbull Basicity matters
bull But compounds protonated to a negligible extentin solution may well ionize
bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular
parameters can distort the picturebull It would certainly work better within compound
familiesbull More data are needed
50
Outlinebull ESI Ionization
bull Mechanismbull Defining the problem
bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method
bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency
bull ESI ionization efficiency and molecular structurebull Still to be done
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
26
51
Still to be donebull Measurements with different MS systems
to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning
parametersbull Preliminary attempts were unsuccessful
52
Still to be donebull More thorough investigation of influence
of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]
bull Different solventsbull Preliminary results show that with common LC-
MS solvent mixtures the picture is similar
Your ideascommentscriticism ismost welcome
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379
27
53
Thanksto all these
people
Funding ESF grant 7127 HTM project SF0180061s08
54Thank you for your attention
bull This talk is available frombull httpterachemutee~ivoChrom_MS
bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379