Ion ChromatographyIon Chromatography

1035510355

Over view

• What is ion chromatography?

• Why this techniqu is useful?

Ion chromatography- definition of terms• Ion exchange- involves exchange of one type of ion in a compound for another. exchange of K+, Ca 2+ and Fe 3+ with Na + in water.• Ion exchange chromatography- involves sequential exchange and elution of ions from a column. Retention is based on attraction between solute ions and charge boundary on the stationary phase.• Ion chromatography- same as ion exchange chromatography except that it includes a provision for removing and detecting (electrochemically) the ions in the eluting agent.

DefinitionsDefinitions

Ion Chromatography is a liquid

chromatographic technique, with

which ionic and strongly polar species

can be separated and detected.

IonIon ChromatographyChromatography System ConfigurationSystem Configuration

EluentEluentReservoirReservoir

PumpPump

Guard ColumnGuard Column

Analytical ColumnAnalytical Column

Suppressor Suppressor DeviceDevice

ConductivityConductivityCellCell

ChromatographyChromatographyWorkstationWorkstation

EluentEluentDeliveryDelivery

AnalyticalAnalyticalSeparationSeparation

DetectionDetection

Data Data Acquisition Acquisition

and and Instrument Instrument

ControlControl

SampleSampleInjectionInjection

11811-0211811-02

Type of Ion Chromatography

• Ion Exchange Chromatography

• Ion Exclusion Chromatography

• Ion Pair (ion Retardation) Chromatography

• Alternative Technique

Advantages of IonAdvantages of Ion ChromatographyChromatography

SpeedSpeed

- Complete anion and cation profiles in about 10 minutes- Complete anion and cation profiles in about 10 minutes

SensitivitySensitivity

-- Analyses in the lowest ppb-range without pre-concentrationAnalyses in the lowest ppb-range without pre-concentration- Analyses in the lowest ppt-range after pre-concentration- Analyses in the lowest ppt-range after pre-concentration- Limiting factor: contaminations by ubiquitous ions such as chloride - Limiting factor: contaminations by ubiquitous ions such as chloride

and sodium and sodium

SelectivitySelectivity

- Huge variety of stationary phases- Huge variety of stationary phases- Specific detection (suppression, UV, fluorescence, MS, ICP)- Specific detection (suppression, UV, fluorescence, MS, ICP)

Advantages of Ion Chromatography (cont.)Advantages of Ion Chromatography (cont.)

SimultaneitySimultaneity

- Simultaneous analysis of many sample components- Simultaneous analysis of many sample components (Contrary: AAS, Photometry, Titration, etc.) (Contrary: AAS, Photometry, Titration, etc.) - - Limiting factor: extreme concentration differences between the sample Limiting factor: extreme concentration differences between the sample components (Example: Semiconductor grade chemicals) components (Example: Semiconductor grade chemicals)

CostsCosts

- Contract laboratories offer anion and cation profiles with IC for US$ 15- Contract laboratories offer anion and cation profiles with IC for US$ 15- Price drop with system hardware as in all hightech areas- Price drop with system hardware as in all hightech areas

RobustnessRobustness

- pH and solvent compatible separators allow a variety of applications- pH and solvent compatible separators allow a variety of applications- Analysis of complex matrices such as waste water, foods, body fluids, etc.- Analysis of complex matrices such as waste water, foods, body fluids, etc.

History

• Aristol experiment(384-322 B.C)• Philasopheres(1561-1626)• Natural Zeolites in soil(1850)• Teoritical research(1876)• First commerical purposes(1896)• First synthetic compound(1903)• First truly successful use(1905)• Synthesise of organic compound(1935) • Use of small particles(1946)

Advantages of organic polymer

• High capasity

• Low sensitivity to temperature and PH

• Provided a back bone for various tyoe

of exchange groups

Making a cation Exchange Resin

Ion exchangers

• Three main classes• Resins

(polystyrene resins; used for molecules with Mr <500)

• Gels (cellulose and dextran; used for large molecules like proteins and nucleic acids)

• Inorganic exchangers (hydrous oxides of Zr,Ti,Sn and W; used for separations under harsh conditions (high temperature, high radiation levels, strongly basic solutions and powerful oxidizing agents)

Resin beads

Exchange functional groups

Cation Exchangers Anion Exchangers

strong -SO3H -N(CH3)3,Cl

-COOH -N(CH3)2CH2OH,Cl

-CH2 SO3H

-OH -NR2H,Cl

-SH -NRH2,Cl

weak -HPO2 H -NH3,Cl

A Lable of a Resin

Sulfonic acid,Na

Mesh:20-50

8X

4.4 meq/g

+

Lable information

Cross-linking Porosity Moisture holding capasity

2X High 85-95

4X IM.High 58-65

8X Medium 44-48

12X IM.Low 40-44

16X Low 37-41

Structure of Sodalite

Different types of ion exchange resins

• Polymeric porous particles

(formed from co-polymerisation of styrene-divinylbenzene)

• Pellicular and superficially porous particles

(formed by coating the ion exchange resin on to an

impervious inert core)

• Totally microporous particles with bonded phases

Pellicular Anion Exchange Bead (Latex)Pellicular Anion Exchange Bead (Latex)

SOSO--33

SOSO--33

SOSO--33

SOSO--33

SOSO--33

SOSO--33

SOSO--33

0.1 0.1 m Diameterm Diameter CoreCoreIon ExchangeIon Exchange

SurfaceSurface

RR33NN++

RR33NN++

NN++RR33

NN++RR33

NN++RR33

RR33NN++

RR33NN++

NN++RR33

NN++RR33

RR33NN++

RR33NN++

NN++RR33

NN++RR33

RR33NN++

RR33NN++

NN++RR33

NN++RR33

31833183--0202

Micro AnionMicro AnionExchange LatexExchange Latex

Sulfonated CationSulfonated CationExchange LatexExchange Latex

MicroporousMicroporous Polymeric PolymericSubstrateSubstrate8.5 mm8.5 mm

55% x-Link55% x-Link

200 200 nmnm

Latex CoatedLatex Coated Pellicular Cation Pellicular Cation Exchangers Exchangers

5606-025606-02

Classification of ion exchangers

• Classified :– by the charge on the stationary phase as:

• anion exchangers-contains positively charged groups• cation exchangers-contains negatively charged groups

– as strongly or weakly acidic or basic:

• strongly acidic cation exchangers eg RSO3-

• weakly acidic cation exchangers e.g RCO2-

• strongly basic anion exchangers e.g RNR’3+

• weakly basic anion exchangers e.g RNR2’H+

Example:

Selectivity and retention in ion exchange analysis

• These are affected by the size and charge of the solvated sample ion.

• Ion exchangers bind strongly to ions with higher charges, lower hydrated radii and higher polarizability

Thus order of selectivity is generally:

Pu 4+ >> La 3+ > Ce 3+ > Pr 3+ > Eu 3+ > Y 3+ > Sc 3+ > Al 3+ >> Ba 2+ > Pb 2+ > Sr 2+ > Ca 2+ > Ni 2 + > Cd 2 + > Cu 2+ > Co 2+ > Zn 2+ > Mg 2+ > UO2 2+ >> Ti + > Ag + > Rb + > K + > NH4 + > Na + > H + > Li +

Retention Determining Parameters (II)Retention Determining Parameters (II)

0 10 20 30 Minutes0

4

µS

F-

Cl-

NO2-

Br-

NO3-

PO43-

SO42-

I-SCN-

S2O32-

0 2 4 6 Minutes 10 0

4

µS

F- Cl-

NO2-

Br-

NO3-

PO43-

SO42-

Monovalent Anions Multivalent Anions

An exception to the rule?

00 1010 2020 3030 MinutesMinutes0

4

µS

F-

Cl-

NO2-

Br-

NO3-

PO43-

SO42-

I-SCN-

S2O32-

S

O

OO

O

2-

S

S

OO

O

2-

Retention Determining Parameters (III)Retention Determining Parameters (III)

Selectivity and retention in ion exchange analysis

• The pH of the mobile phase

• The total concentration and type of ionic species in the mobile phase

• Addition of organic solvents to the eluant

• The column temperature

PH of the mobile phase

Concentration

Ion Exchange Kinetics

• There are 5 main steps:• 1)agiated• 2)passage from the outer

solution to the bead• 3)actual exchange• 4)migration • 5)exit to the mobile

phase

Donnan equilibrium

• Refers to the equilibrium between ions in solution and ions inside the resin. This is the basis of ion-exclusion chromatography.

• For an anion-exchange resin, R+, in its Cl- form, immersed in a solution of KCl:

[K+]i [Cl-]i = [K+]o[Cl-]o --------(1) where i and o denote inside and outside the resin respectively.

• Inside the resin,

[R+]i + [K+]i = [Cl-]i -------(2)• Since from charge balance :

[K+]o = [Cl-]o

• considerations, equation (1) becomes :

[K+]i([R+]i + [K+]i ) =[K+]o2 ------------(3)

• Thus

[K+]o > [K+]i

Porous particlate andMicro porous membrane

FASTCHROM standard module and end plates

Applications of Ion exchange

• In water purification.– Deionised water is made by passing water through a anion-

exchange in it OH- form and a cation-exchange resin in its H+ form.

– Thus Cu(NO3)2 can be removed from water by the following reactions

• Cu 2+ H+ ion exchange 2H+ H2O• 2NO3- OH- ion exchange 2OH-}

• In water softeners– Cation exchange is used to remove Ca 2+ and Mg 2+ from

hard water• In converting one salt to another.• In pre-concentrating trace components of a mixture

– Cation-exchange resins are used to concentrate trace metals..

Ion chromatography

• This is the high performance version of IEC.• Common examples are:

– Suppressed cation chromatography and– Suppressed anion chromatography

• The key feature of IC is the presence of– an anion or cation separator column– a membrane ion suppressor– a detector

• The separator column separates the solutes while the suppressor replaces unwanted ions in the eluent with nonionic species

The Instrument

• COST: $40,000

Operation Principles

Eluent from the gradient pump enters the rheodyne injection valve port inside the enclosure

From the injection valve, eluent and sample flow through the guard column, the analytical column, the suppressor and finally through the detector cell.

The IC Schematic

• Pump, Column ($800), Guard ($200)• Air Pump for sample injection

Schematic of a Loop InjectorSchematic of a Loop Injector

11

22

33

44

55

6688

77

EluentEluent

WasteWaste

SeparatorSeparator

SampleSample

Injection valveInjection valve

Sample loopSample loop

Ion Chrom. for analysis of rain

• If inject sample with nitrate ion, nitrate replaced bicarbonate, but more bicarbonate moves in and kicks off nitrate

• Process continues as moves through column (ions go on and off beads)

• Sulfate in sample as well. Harder for bicarbonate to knock off.

• Conclude: Nitrate exits before Sulfate

Ion Chrom.

• See Peaks (Rain has nitrate, sulfate, some chloride)

IC Report

14209

EluentsEluents(NaOH, H(NaOH, H22SOSO44))

ChromatogramChromatogram

PumpPump

SuppressorSuppressor

ColumnColumn

InjectorInjector

Conductivity CellConductivity Cell

What is an IC?What is an IC?

RegenerantRegenerant

(H(H22SOSO44, TBAOH), TBAOH)

WasteWaste

Separation of Common Anions on the IonPacSeparation of Common Anions on the IonPac AS14 AS14

Column:Column: IonPac AG14, AS14 IonPac AG14, AS14Eluent:Eluent: 4.8 mM Sodium carbonate4.8 mM Sodium carbonate

0.6 mM Sodium bicarbonate0.6 mM Sodium bicarbonateFlow Rate: Flow Rate: 1.5 mL/min1.5 mL/minInj. Volume:Inj. Volume: 10 10 LLDetection:Detection: Suppressed conductivity, ASRS, Suppressed conductivity, ASRS,

AutoSuppressionAutoSuppression recycle mode recycle modePeaks:Peaks: 1.1. FluorideFluoride 5 5 mg/Lmg/L

2.2. ChlorideChloride 10103.3. NitriteNitrite 15154.4. BromideBromide 25255.5. NitrateNitrate 25256.6. PhosphatePhosphate 40407.7. SulfateSulfate 3030

1172411724

00

10 10

00 11 22 33 44 55 66 77 88 99MinutesMinutes

1122

33 44 55

66

77

Suppression:Suppression:

Reducing the background conductance due to the eluent to aReducing the background conductance due to the eluent to alow level while enhancing the conductance of the analyte.low level while enhancing the conductance of the analyte.

8140-018140-01

Small et al. PublishSmall et al. Publish1st IC Paper1st IC PaperPacked BedPacked BedSuppressionSuppression

CommercializedCommercialized

Fiber SuppressionFiber SuppressionCommercializedCommercialized

MicroMembraneMicroMembrane

SuppressorsSuppressorsIntroducedIntroduced

AutoRegenAutoRegen

IntroducedIntroduced

SRSSRS®® -I -IAutoSuppressionAutoSuppression®®

IntroducedIntroduced

2-2-mmmmMicroMembraneMicroMembrane

SuppressorsSuppressorsIntroducedIntroduced

SRS-IISRS-IIIntroducedIntroduced

19811981 19851985 19871987 19911991 19921992 1997199719751975

SRS-ULTRASRS-ULTRASuppressorsSuppressorsIntroducedIntroduced

19981998

Suppression Time LineSuppression Time Line1975 - 19981975 - 1998

11136-0211136-02

11309-0111309-01

The Role of Chemical SuppressionThe Role of Chemical Suppression

EluentEluent(NaOH)(NaOH)

Sample FSample F --, CI, CI --, SO, SO442-2-

AnalyticalAnalyticalColumnColumn(Anion(Anion

Exchanger )Exchanger )

AnionAnionSuppressorSuppressor

(Cation(CationExchanger)Exchanger)

HF, HCI, HHF, HCI, H22SOSO44in Hin H22OO

NaF, NaCI,NaF, NaCI,NaNa22SOSO44 in inNaOHNaOH

WasteWaste

H+H+

Without SuppressionWithout Suppression

Counter IonsCounter Ions

SS

F-F-

SOSO442-2-

CICI--

F-F- SOSO442-2-

TimeTime

SS

TimeTime

With Chemical SuppressionWith Chemical Suppression

CICI--

NaNa++

What are Suppressors in Ion Chromatography What are Suppressors in Ion Chromatography Good For ?Good For ?

• To reduce background conductance caused by the eluent and, therefore, to reduce noise

• To convert analyte ions into a more strongly conducting form

• To improve sensitivity • To improve the dynamic range• To be able to use high capacity separators with

higher ionic strength eluents• To be able to use gradient elution techniques in

combination with conductivity detection

Advantages of Continuous SuppressionAdvantages of Continuous Suppression

• Improved stability of the system

• Very little drift and low noise

• High suppression capacity

• No external regeneremts necessary

• Simple operation – no extra programming

• Simplified hardware – no extra valves

• Flexible method development

Equivalent Conductances of Common IonsEquivalent Conductances of Common Ions

AnionsAnions CationsCations

IonIon 00((µµS cmS cm 11)) IonIon 00((µµ S cmS cm 11))

OHOH 198.6198.6 HH++ 349.8349.8

CICI 76.476.4 NaNa++ 50.150.1

SOSO4422 80.080.0 KK++ 73.573.5

NONO33 71.571.5

MSAMSA 48.848.8

**MSAMSA--: Methanesulfonate: Methanesulfonate

Suppression replaces eluent counterions with more highly conducting HSuppression replaces eluent counterions with more highly conducting H++ or orOHOH-- ions ions

Self Regenerating Suppressor SchematicSelf Regenerating Suppressor Schematic(Ion Exchange Membrane - Continuous Regeneration)(Ion Exchange Membrane - Continuous Regeneration)

12442-0112442-01

Na+OH-

(Eluent)

Na+Cl-(Sample)

HOH(Eluent)

H+Cl-(Sample)

ConductivityDetector

Cation Exchange Membrane in HCation Exchange Membrane in H++ form form

Waste

Regenerating ElectrodeRegenerating Electrode

Eluent RecycleEluent Recycle

H2O

H+Na+

Na+

H+ O2

-e

+

DetectorDetectorCellCell

WasteWaste

EluentEluentSRSSRS

RecycledRecycledto SRSto SRS

1431143155

Eluents: Eluents: ASRSASRS —— Hydroxide, carbonate/bicarbonate Hydroxide, carbonate/bicarbonate

CSRSCSRS —— Methanesulfonic Methanesulfonic acid (MSA), sulfuric acid acid (MSA), sulfuric acid

--

++

SRSSRS AutoSuppression AutoSuppression

Recycle ModeRecycle Mode

DetectorDetectorCellCell

WasteWaste

EluentEluentSRSSRS

1431714317

Eluents: Eluents: ASRSASRS —— Hydroxide, carbonate/bicarbonate Hydroxide, carbonate/bicarbonate

CSRSCSRS —— Methanesulfonic Methanesulfonic acid (MSA), sulfuric acid acid (MSA), sulfuric acid

--

++

WasteWaste

H2SO4 or TBAOH(P)

SRSSRS Chemical Regeneration Mode Chemical Regeneration Mode

AutoSuppression Using Anion SRSAutoSuppression Using Anion SRS

8482-8482-BB

AnodeWaste/Vent

H2O, O2

Na+X- in Na+ OH- Eluent

Na+OH-

Waste/VentCathode

Na+ OH- , H2

H2 + OH-

H2O

H2O

CationExchangeMembrane

CationExchangeMembrane

To Detector

H+ + O2

H2O

H2O

H+

H2O

H+X-H+ + X-

H+ + OH-

H+X- in H2O

AutoSuppression Using the Cation SRSAutoSuppression Using the Cation SRS

8483-018483-01

AnodeWaste/Vent

H+MSA-, O2

M+MSA- in H+MSA- EluentWaste/Vent

Cathode

H2O , H2

OH-

H2 + OH-

H2O

H2O

AnionExchangeMembrane

AnionExchangeMembrane

To Detector

H+ + O2

H2O

H2O

H+

H2O

M+OH-H+ + X-

H+ + OH-

M+OH- in H2O

H+MSA- = Methanesulfonic Acid

MSA-

Single ion chromatography

• Used when– Exchange capacity of the separator column is low– Dilute eluents are employed– Ion suppression is unnecessary

• Examples of resins with low exchange capacities are:– Na + or K + salts of benzoic, p-hydroxybenzoate and

phthalate.

Gradient elution

• Ionic gradient elution is similar to temperature or solvent gradient.

• Changing the ionic strength or pH of the eluent improves separation considerably.

• For example, a mixture of Na+, Li+, Ca 2+ and Fe 3+ can be separated by using elution with increasing concentrations of HCl.

• The order of elution being Li +, Na + > Ca 2+ > Fe 3+

Gradiant separation of a synthetic mixture of 36 anions in 24 min.

Advantages of UsingAdvantages of Using Eluent Generators in Ion Chromatography Eluent Generators in Ion Chromatography

Requires only deionized water as the carrierRequires only deionized water as the carrier

Generates high-purity, contaminant free acidGenerates high-purity, contaminant free acidand base eluents on-lineand base eluents on-line

Eluent concentration controlled electricallyEluent concentration controlled electricallywith minimal delaywith minimal delay

Improved retention time reproducibilityImproved retention time reproducibility

Minimize pump maintenanceMinimize pump maintenance

1429714297

Gradiant Elution

Detector in Chromatography

• Electrochemical Detector - Conductivity Detector - Amperometric Detector

- Pulsed Amperometric Detector

• Spectroscopy Detector - UV/Vis - Fluorescence - PDA

Detection

• Conductivity detectors are the most popular• In addition, when analytes have

– Ultraviolet absorbance– Fluorescence or– Radioactivity other forms of detection are employed.

• Many ion exchange methods require the presence of complexing agents (EDTA, citrate) and various electrolytes to achieve good resolution. Therefore, conductivity detectors can not be used without modifying the process (eg by suppressing some of the ions).

• Indirect detection is possible when benzoate or phthalate eluents are used.

The Altec model 1000 electrochemical regenerated ion suppression system

and Sample preconcentrator

IC conductivity Detectors

• Detectors: Based on ability of water to conduct electricity

• Suppressor membrane destroys bicarbonate only

• Conductivity of ions can be measured to very low levels

Electrochemical palsed amperometric cell assembly

5031-025031-02

Triple Potential Sequence Used inTriple Potential Sequence Used inPulsed AmperometryPulsed Amperometry

PotentialPotential

IntegrationIntegrationDelayDelay

E2E2

E1E1E3E3

t3t3

t2t2

TimeTime

Column size PH range capasity Particle size Type of packing mm µm

Vydac 250x4.6 2-6 100 20 spherical silica with IC bonded quaternary groups

INtraction 50x3.2 0-14 100 10 Neutral hydrophilic Ion100 narymacroporous resin with covalentlyi bond ammonium groups

Hamilton 150x4.1 1-13 200 10 Highly crosslinked -X100 covalentlyi bond ammonium groups

Bio-GelTSX 50x4.6 1-12 30 10 Polymetacrilat gel coated with Anion PW quaternaryammonium groups

Waters ic 50X4.6 1-12 30 10 Same Pak A

One chromatogram with 5 detector

Ion-pair chromatography

• Uses reverse phase HPLC in place of an ion exchange column

• A hydrophobic ion pairing reagent containing a counter-ion, with an opposite charge to the ion to be determined is added to the mobile phase.

• This counter ion combines with the ions of the eluent to form ion pairs in the stationary phase.

• For example, Fe(phen)3 2+ forms [Fe(phen)3

2+ ] [anion] ion pair.

• Retention of analytes depend on– Alkyl chain length of the counter-ion– Concentration of the ion pairing reagent– Solvent strength– Combination with ion suppressor

Ion Exchange ChromatographyIon Exchange Chromatography

Mechanism of RetentionMechanism of Retention

11229

StationaryPhase

NR3+

S

S

MobilePhase

S

Mechanism of Anion Ion-PairingMechanism of Anion Ion-Pairing

1280712807

Eluent: TBAOH/ACN/HEluent: TBAOH/ACN/H22OOSample: Anions (A)Sample: Anions (A)

HydrophilicHydrophilicEnvironmentEnvironment

HydrophobicHydrophobicEnvironmentEnvironment

ACNACN

TBATBA++ __AA

ACNACN

TBATBA++ __AA

ACNACN

TBATBA++ __AA

TBATBA++ __AA

NeutralNeutralMacroporousMacroporous

Resin (PS/DVB)Resin (PS/DVB)

TBATBA++ OH OH __

ACN: AcetonitrileACN: AcetonitrileTBAOH: Tetrabutylammonium hydroxideTBAOH: Tetrabutylammonium hydroxide

((TBATBA++ __A)A)

TBATBA++ OH OH __

HH22OO

ACNACN

((TBATBA++ __A)A)

HH22OO

ACNACN

Separation of Aliphatic Sulfonic AcidsSeparation of Aliphatic Sulfonic AcidsUsing Ion-Pairing with Suppressed ConductivityUsing Ion-Pairing with Suppressed Conductivity

11140-0111140-01

Column:Column: IonPac NS1 (10 IonPac NS1 (10 탆탆))Eluent:Eluent: 2 mM Tetrabutylammonium hydroxide,2 mM Tetrabutylammonium hydroxide,

24% to 48% Acetonitrile in 10 min24% to 48% Acetonitrile in 10 minFlow Rate:Flow Rate: 1.0 mL/min1.0 mL/minInj.Volume:Inj.Volume: 50 50 킠킠Detection:Detection: Suppressed conductivitySuppressed conductivity

ASRS AutoSuppressionASRS AutoSuppression,,external water modeexternal water modeRegenerant:Regenerant: 10 mN Sulfuric acid10 mN Sulfuric acidPeaks:Peaks: (as the acid forms)(as the acid forms)

1. Methanesulfonic acid1. Methanesulfonic acid 5.0 mg/L (ppm)5.0 mg/L (ppm)2. 1-Propanesulfonic acid2. 1-Propanesulfonic acid 8.68.63. 1-Butanesulfonic acid3. 1-Butanesulfonic acid 8.78.74. 1-Hexanesulfonic acid4. 1-Hexanesulfonic acid 8.88.85. 1-Heptanesulfonic acid5. 1-Heptanesulfonic acid 8.98.96. 1-Octanesulfonic acid6. 1-Octanesulfonic acid 8.98.97. 1-Decanesulfonic acid7. 1-Decanesulfonic acid 9.19.1

11

66

66

22 33

00MinutesMinutes

121222 1414 161688

킪킪

0.00.0

44

44 55

77

8.08.0

1010

Schematic of Ion Exclusion MechanismSchematic of Ion Exclusion Mechanism

99639963

Mobile Phase

Donnan-Membrane

Stationary PhaseH220

H++Cl--

H220

H220

H220

SO33--H++

SO33--H++

SO33--H++

SO33--

H220

SO33--

H220

--

H++

(Eluent)

CH33COOHH++

Example for separation with regeneration

…THE …END…

…THE …END…