The Royal Society of Chemistry - Negative Electrospray Ionization … · 2014. 1. 6. · 1...

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Electronic Supplementary Information

Negative Electrospray Ionization on Porous Supporting Tips for

Mass Spectrometric Analysis: Electrostatic Charging Effect on

Detection Sensitivity and Its Application to Explosive Detection

Melody Yee-Man Wonga, Sin-Heng Man

a, Chi-Ming Che

a, Kai-Chung Lau

b, Kwan-Ming Ng*

a

a Department of Chemistry, and State Key Laboratory of Synthetic Chemistry, The University of

Hong Kong, Pokfulam Road, Hong Kong SAR, People’s Republic of China

b Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Hong

Kong SAR, People’s Republic of China

To whom correspondence should be addressed:

K.-M. Ng

Fax: (852) 2857 1586 ; E-mail: [email protected]

Electronic Supplementary Material (ESI) for AnalystThis journal is © The Royal Society of Chemistry 2014

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Table S1. Elemental (CH) composition analysis of fibers of polyester tips and granules of polyethylene tips performed by the Institute of

Chemistry, Chinese Academy of Sciences, Beijing, China.

Weight Percentage of Carbon Weight Percentage of Hydrogen

Measured Theoretical Measured Theoretical

Polyester

H-(C10H8O4)n-OH 60.81% 62.50% 4.87% 4.20%

Polyethylene

H-(C2H4)n-H 85.11% 85.63% 12.97% 14.37%


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Table S2. The effect of the hydrolysis and the in-source fragmentation (i.e., NO loss) on the total ion intensities of nitrobenzene derivatives using polyethylene supporting tips.

[M]-‧

, Molecular Ion [M – NO]-‧

, Fragment Ion Hydrolyzed Product

Total Ion Intensity

a

Correction Factorb

Ratio: Total Ion Intensity/[M]-‧

m/z (Ion Intensity) m/z (Ion Intensity) m/z (Ion Intensity)

NB 123.0 (953) 92.9 (5491) NDc 6444 6.762

4-NT 137.0 (124) 106.9 (183) NDc 307 2.476

1-F-4-NB 141.0 (17822) 111.0 (1425) 138.0d (4667) 23914 1.342

1-Cl-4-NB 157.0 (7368) 127.0 (1575) 138.0d (2018) 10961 1.488

1,3-DNB 168.0 (11664) 138.0 (7974) NDc 19638 1.684

2,4-DNT 182.0 (870) 152.0 (285) NDc 1155 1.328

1-F-2,4-DNB 186.0 (28180) 156.0 (10621) 182.9e (10618) 49419 1.754

1-Br-4-NB 200.9 (455) 171.1 (526) 138.0d (689) 1670 3.670

1-Br-2,4-DNB 245.9 (199) 215.9 (205) 182.9e (2760) 3164 15.90

1-I-4-NB 248.9 (219) 218.9 (97) 138.0d (1844) 2160 9.863

1-I-2,4-DNB 293.8 (4727) 263.8 (4162) 182.9e (22946) 31835 6.735

a total ion intensity is the sum of [M]

-‧, [M – NO]

-‧ and deprotonated ion of the hydrolyzed product (if any);

b correction factor is used to determine the corrected total ion intensity for the correlation with electron affinities of

nitrobenzene derivatives; c ND stands for not detected;

d the ion peak at m/z 138.0 corresponds to the deprotonated ion of the hydrolyzed product of 1-F-4-NB, 1-Cl-4-NB, 1-Br-4-NB and 1-I-4-NB formed via nucleophilic

substitution reaction; e the ion peak at m/z 182.9 corresponds to the deprotonated ion of the hydrolyzed product of 1-F-2,4-DNB, 1-Br-2,4-DNB and 1-I-2,4-DNB formed via nucleophilic substitution reaction.


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Table. S3. The effect of the hydrolysis and the in-source fragmentation (i.e., NO loss) on the total ion intensities of nitrobenzene derivatives using polyester supporting tips.

[M]-‧

, Molecular Ion [M-NO]-‧

, Fragment Ion Hydrolyzed Product Total

Ion Intensitya

Correction Factorb

Ratio: Total Ion Intensity/[M]-‧

m/z (Ion Intensity) m/z (Ion Intensity) m/z (Ion Intensity)

NB 123.0 (67) 93.0 (1075) NDc 1142 17.04

4-NT 137.0 (67) 107.0 (1151) NDc 1218 18.18

1-F-4-NB 140.9 (1042) 110.9 (556) 138.0d (320) 1918 1.841

1-Cl-4-NB 156.9 (3932) 126.9 (7929) 138.0d (370) 12231 3.111

1,3-DNB 168.0 (5387) 138.0 (409) NDc 5796 1.076

2,4-DNT 182.0 (2285) 152.0 (470) NDc 2755 1.206

1-F-2,4-DNB 186.0 (5108) 156.0 (1910) 183.0e (1981) 8999 1.762

1-Br-4-NB 200.9 (227) 170.9 (68) 138.0d (1285) 1580 6.960

1-Br-2,4-DNB 245.9 (142) 215.9 (221) 183.0e (6277) 6640 46.76

1-I-4-NB 248.9 (100) 218.9 (31) 138.0d (981) 1112 11.12

1-I-2,4-DNB 293.8 (438) 263.9 (682) 183.0e (4526) 5646 12.89

a total ion intensity is the sum of [M]

-‧, [M-NO]

-‧ and deprotonated ion of the hydrolyzed product (if any);

b correction factor is used to determine the corrected total ion intensity for the correlation with electron affinities of

nitrobenzene derivatives; c ND stands for not detected;

d the ion peak at

m/z 138.0 corresponds to the deprotonated ion of the hydrolyzed product of 1-F-4-NB, 1-Cl-4-NB, 1-Br-4-NB and 1-I-4-NB via nucleophilic substitution

reaction; e the ion peak at m/z 183.0 corresponds to the deprotonated ion of the hydrolyzed product of 1-F-2,4-DNB, 1-Br-2,4-DNB and 1-I-2,4-DNB via nucleophilic substitution reaction.


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Table S4. Theoretically calculated and experimentally determined electron affinities of nitrobenzene derivatives.

Compounds

Electron affinity (eV)

G4 Literature |ΔG4 -Lit|

Nitrobenzene 1.06 1.00 ± 0.01a 0.06

4-Nitrotoluene 0.99 0.93 ± 0.09b 0.06

1-Fluoro-4-nitrobenzene 1.13 1.08 ± 0.09b 0.05

1-Chloro-4-nitrobenzene 1.27 1.23 ± 0.09b 0.04

1-Bromo-4-nitrobenzene 1.32 -- --

1,3-Dinitrobenzene 1.65 1.66 ± 0.10c 0.01

2,4-Dinitrotoluene 1.58 -- --

1-Fluoro-2,4-dinitrobenzene 1.71 -- --

1-Chloro-2,4-dinitrobenzene 1.78 -- --

1-Bromo-2,4-dinitrobenzene 1.80 -- --

a C. Desfrancois, V. Periquet; S. A. Lyapustina.; T. P. Lippa; D. W. Robinson; K. H. Bowen; H. Nonaka and Compton, J. Chem. Phys.,

1999, 111, 4569 - 4576

b C. Huh; C. H. Kang; H. W. Lee; H. Nakamura; M. Mishima; Y. Tsuno and H. Yamataka, Bull. Chem. Soc. Japan, 1999, 72, 1083-1091

c S. Chowdhury; T. Heinis; E. P. Grimsrud; P. Kebarle, J. Phys. Chem., 1986, 90, 2747 - 2752

|ΔG4 -Lit| means the absolute difference between the calculated EA (using G4 theory) and the EA obtained from the literature.


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Table. S5. The effect of in-source fragmentation (i.e., NO loss) on the total ion intensities of nitrophenol derivatives using polyethylene supporting tips.

[M – H]-, Molecular Ion [M – H – NO]

-, Fragment Ion Total

Ion Intensity a

Correction Factor b

Ratio: Total Ion Intensity/[M-H]- m/z (Ion Intensity) m/z (Ion Intensity)

4-NPh 138.0 (9408) 108.0 (6600) 16008 1.702

2-Me-4-NPh 152.0 (4283) 122.0 (2818) 7101 1.658

2-F-4-NPh 156.0 (27870) 126.0 (4626) 32496 1.166

2,6-DMe-4-NPh 166.0 (5545) 136.0 (2100) 7645 1.379

2-Cl-4-NPh 172.0 (10967) 142.0 (427) 11394 1.039

2,6-DF-4-NPh 174.0 (15834) 144.0 (2712) 18546 1.171

2,4-DNPh 183.0 (201701) 153.0 (19645) 221346 1.097

2,6-DCl-4-NPh 205.9 (18480) 175.9 (1685) 20165 1.091

2-Br-4-NPh 215.8 (8934) 186.0 (2466) 11400 1.276

2,4,6-TNPh 227.9 (17982) 197.9 (6218) 24200 1.346

2-I-4-NPh 263.9 (5767) 233.9 (622) 6389 1.108

2,6-DBr-4-NPh 293.7 (5684) 263.8 (38) 5722 1.007

2,6-DI-4-NPh 389.7 (4554) 359.7 (269) 4823 1.059

a Total ion intensity is the sum of [M – H]

- and [M – H – NO]

-;

b correction factor is used to determine the corrected total ion intensity for the correlation with pKa of nitrophenol derivatives.


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Table. S6. The effect of in-source fragmentation (i.e., NO loss) on the total ion intensities of nitrophenol derivatives using polyester supporting tips.

[M-H]-, Molecular Ion [M-H-NO]

-, Fragment Ion

Total Ion Intensity

a

Correction Factorb

Ratio: Total Ion Intensity/[M-H]-

m/z (Ion Intensity) m/z (Ion Intensity)

4-NPh 138.0 (13476) 108.0 (5200) 18676 1.386

2-Me-4-NPh 152.0 (19742) 122.0 (2294) 22036 1.116

2-F-4-NPh 156.0 (9626) 126.0 (1955) 11581 1.203

2,6-DMe-4-NPh 166.0 (4874) 136.0 (784) 5658 1.161

2-Cl-4-NPh 171.9 (8611) 141.9 (333) 8944 1.039

2,6-DF-4-NPh 173.9 (21574) 144.0 (4335) 25909 1.201

2,4-DNPh 182.9 (6325) 153.0 (413) 6738 1.065

2,6-DCl-4-NPh 205.9 (7282) 175.9 (599) 7881 1.082

2-Br-4-NPh 215.9 (1146) 186.0 (549) 1695 1.479

2,4,6-TNPh 227.9 (14045) 198.0 (3415) 17460 1.243

2-I-4-NPh 263.8 (40831) 233.8 (184) 41015 1.005

2,6-DBr-4-NPh 293.7 (17322) 263.8 (157) 17479 1.009

2,6-DI-4-NPh 389.7 (10888) 359.7 (67) 10955 1.006

atotal ion intensity is the sum of [M-H]

- and [M-H-NO]

-;

b correction factor is used to determine the corrected total ion intensity for the correlation with pKa of nitrophenol derivatives.


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Table S7. Theoretically calculated gas phase acidities (Gibbs free energy change of deprotonation), acid dissociation constant from

the literature and theoretically calculated electron affinities of nitrophenol derivatives.

a MH M

- + H

+, ΔGdeprotonation = G(M

-) + G(H+) – G(MH)

b J. A. Dean, Lange's Handbook of Chemistry, 15

th edition, McGraw-Hill, Inc

c M + e M

.-, EA = E(M) – E(M

.-)

Compounds

Gas Phase Acidity a

at 298K (kJ/mol)

Acid Dissociation

Constant at 298K (pKa)b

Electron affinityc

at 0 K (eV)

G4 theory G4 theory

4-Nitrophenol 1343.3 7.15 0.93

2-Methyl-4-nitrophenol 1341.8 7.43 0.90

2-Fluoro-4-nitrophenol 1330.7 5.70 1.13

2-Chloro-4-nitrophenol 1327.1 6.48 1.16

2-Bromo-4-nitrophenol 1323.3 -- 1.18

2,4-Dinitrophenol 1312.6 4.08 2.10

2,6-Dimethyl-4-nitrophenol 1340.4 7.19 0.88

2,6-Difluoro-4-nitrophenol 1310.4 -- 1.33

2,6-Dichloro-4-nitrophenol 1301.8 6.79 1.36

2,6-Dibromo-4-nitrophenol 1295.9 -- 1.39

2,4,6-Trinitrophenol 1254.5 0.42 (at 291K) 2.74


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Fig. S1. Infrared spectrum of a thin film made of the materials obtained from polyester tips.


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Fig. S2. Infrared spectrum of a thin film made of the materials obtained from polyethylene tips.


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Fig. S3. (a) (i) ESI mass spectrum of hydrolyzed product of polyester tips; (ii) magnified mass spectrum of (i); and (iii) simulation

spectrum of deprotonated terephalate [C8H6O4 – H]-. (b) Tandem mass spectra of (i) [C8H6O4 – H]

- at m/z 165.0; and (ii) [C8H6O4 –

CO2 – H]- at m/z 121.0. Collision energy of (b) (i) and (ii) were set at 15.0 eV and 6.0 eV, respectively.


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Fig. S4. Nuclear magnetic resonance (NMR) spectrum of hydrolyzed

product of polyester tips.


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Fig. S5. Contact angle of a water droplet on (a) polyester thin film; and (c) polyethylene thin film. (b) and (d) are the magnified

images of (a) and (c), respectively.


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Fig. S6. Detection of background ions (CH3O-·, O2

-· and HO2

-·) by

negative tip spray ionization mass spectrometry.


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Fig. S7. Detection of 1,4-benzoquinone by negative tip spray

ionization mass spectrometry.


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Fig. S8. (a) Detection of (i) 1-bromo-4-nitrobenzene (1-Br-4-NB) and (ii) 1-bromo-2,4-dinitrobenzene (1-Br-2,4-DNB) by negative tip

spray ionization mass spectrometry. (b) Bromide ions were simultaneously detected, indicating that fragmentation of (i) 1-Br-4-NB and

(ii) 1-Br-2,4-DNB occurred in electron capture ionization.


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Fig. S9. (a) Detection of (i) 1-iodo-4-nitrobenzene (1-I-4-NB) and (ii) 1-iodo-2,4-dinitrobenzene (1-I-2,4-DNB) by negative tip spray ionization

mass spectrometry. (b) Iodide ions were simultaneously detected, indicating that fragmentation of (i) 1-I-4-NB and (ii) 1-I-2,4-DNB occurred in

electron capture ionization.


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Fig. S10. Material effect on the onset voltage and sensitivity for the

detection of (a) 1-fluoro-2,4-dinitrobenzene (1-F-2,4-DNB) and (b)

1-chloro-2,4-dinitrobenzene (1-Cl-2,4-DNB) by negative tip spray

ionization mass spectrometry.


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(a) 1,3-DNB

(b) 1-F-2,4-DNB (c) 1-Cl-2,4-DNB

Fig. S11 Material effect on the onset voltage and sensitivity for the detection of (a) 1,3-dinitrobenzene (1,3-DNB), (b) 1-fluoro-2,4-dinitrobenzene

(1-F-2,4-DNB), and (c) 1-chloro-2,4-dinitrobenzene (1-Cl-2,4-DNB) by negative tip spray ionization mass spectrometry and ESI-MS.


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Fig. S12. Triboelectric series for organic polymers.

[Ref: A. F. Diaz and R. M. Felix-Navarro, J

Electrostat., 2004, 62, 277–290].


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Fig. S13. Correlation of ion intensities of deprotonated nitrophenol

compounds with their respective gas-phase acidities. 2,4,6-TNPh:

2,4,6-trinitrophenol; 2,6-DBr-4-NPh: 2,6-dibromo-4-nitrophenol;

2,6-DCl-4-NPh: 2,6-dichloro-4-nitrophenol; 2,4-DNPh:

2,4-dinitrophenol; 2-Br-4-NPh: 2-bromo-4-nitrophenol; 2-Cl-4-NPh:

2-chloro-4-nitrophenol; 2-F-4-NPh: 2-fluoro-4-nitrophenol; 4-NPh:

4-nitrophenol; 2,6-DMe-4-NPh: 2,6-dimethyl-4-nitrophenol;

2-Me-4-NPh: 2-methyl-4-nitrophenol.


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Fig. S14. Material effect on the onset voltage and detection sensitivity

for (a) 2-fluoro-4-nitrophenol (2-F-4-NPh) and (b) 2-chloro-4-nitrophenol

(2-Cl-4-NPh).


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Fig. S15. Chemical structures of spraying tip materials: (a) wood;

(b) polyester; and (c) polyethylene.


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(a) 4-NPh

(b) 2-F-4-NPh (c) 2-Cl-4-NPh

Fig. S16 Material effect on the onset voltage and sensitivity for the detection of (a) 4-nitrophenol (4-NPh), (b) 2-fluoro-4-nitrophenol (2-F-4-NPh)

and (c) 2-chloro-4-nitrophenol (2-Cl-4-NPh) by negative tip spray ionization mass spectrometry and ESI-MS.


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Fig. S17. Linear calibration curve of 2,4-dinitrotoluene (2,4-DNT)

recorded by negative tip spray ionization mass spectrometry.

1,3-dinitrobenzene (1,3-DNB) at 2x10-5

M was used as internal

standard.


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Fig. S18. Tandem mass spectrum of (a) 0.4 ppm 2,4-dinitrotoluene

(2,4-DNT) spiked in soil extract; and (b) 2,4-DNT standard. (collision

energy at 6eV, laboratory frame)


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Fig. S19. Tandem mass spectrum of (a) 20 ppm of

2,4,6-trinitrophenol (2,4,6-TNPh) spiked in soil extract; and

(b) 2,4,6-TNPh standard. (collision energy at 20eV, laboratory

frame)


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Fig. S20. (a) (i) Total ion chromatogram; (ii) extracted ion chromatograms for 2,4-DNT at m/z 182.0, 1-F-4-NB at m/z 141.0 and

1,3-DNB at m/z 168.0; (iii) mass spectrum at the 5th minute; and (iv) mass spectrum at the 20

th minute of the detection of

nitrobenzene radical anions using polyethylene supporting tips; and (b) (i) total ion chromatogram; (ii) extracted ion

chromatograms for 2,4-DNT at m/z 182.0, 1-F-4-NB at m/z 141.0 and 1,3-DNB at m/z 168.0; (iii) mass spectrum at the 5th minute;

and (iv) mass spectrum at the 20th minute of the detection of nitrobenzene radical anions using polyester supporting tips.


The Royal Society of Chemistry - Negative Electrospray Ionization … · 2014. 1. 6. · 1...

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