Capillary Ion Chromatography Mass Spectrometry for Trace Environmental Analysis Leo Jinyuan Wang,1 Jonathan Beck,2 and William C. Schnute1 1Thermo Fisher Scientific, Sunnyvale, CA, USA; 2Thermo Fisher Scientific, San Jose, CA, USA

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Executive SummaryCapillary IC-MS offers unique chromatographic selectivity for polar analytes and can be used as a complementary technique to reversed phase LC-MS in trace level analysis. Compared to conventional IC, capillary IC offers higher mass sensitivity, reduces eluent consumption, decreases waste, and allows continuous system operation, ultimately leading to reductions in total cost of ownership. Coupling capillary IC to MS detection requires modification and optimization of existing electrospray ionization (ESI) interfaces. Optimized configurations enable highly sensitive and selective determination of ppt to low ppb levels of analytes in environmental samples.

IntroductionIC has been used extensively as a complementary separation technique to high performance liquid chromatography (HPLC). Recent applications include coupling to MS for identity confirmation, structural interpretation, and trace level analysis in complex matrices. The introduction of innova-tive capillary IC further improves the usability of IC-MS for trace-level analysis and sample- size-limited research such as in metabolism/metabolomics. The main challenges of interfacing capillary IC and MS are compatibilities in mobile phase composition and flow rate. This study demonstrates the instrumentation and application solutions for capillary IC-MS utilizing a Thermo Scientific™ Dionex™ ICS-5000 Reagent-Free™ IC (RFIC™) system with suppression technology which converts the MS-incompatible mobile phase to deionized (DI) water, and a modified ESI source which optimizes capillary flow sensitivity.

Using capillary IC with an RFIC system in conjunction with the optimized ESI source, this study demonstrates successful applications for trace level environmental analysis, including common anions and organic acids, perchlorate, and residue of the herbicide endothall in environmental water samples.

Key WordsCapillary IC, IC-MS, Environmental analysis, ICS-5000 RFIC

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Capillary IC-MS Interface OptimizationThe optimization of the capillary IC-MS interface was deemed to be a necessity and of paramount importance for system detection sensitivity. Commercially available interfaces can be divided into two categories based on compatible flow rate ranges: nano-ESI sources usually cover flow rates below 1 µL/min; analytical ESI interfaces are designed for a broad flow rate range of 1 to 2000 µL/min, generally with higher performance in the range of 50 to 1000 µL/min.

A Thermo Scientific Ion Max source was selected for this study as shown in Figure 2. The parameters related to sensitivity include: the diameter of the ESI spray capillary; the proximity of the spray capillary tip to the MS entrance (controlled by probe depth and probe x-y-z adjustments); the ESI voltage; vaporizer and transfer capillary temperatures; and gas flows including sheath, auxiliary, and ion sweep gases.

Figure 1. Preferred capillary IC-MS system schematics.

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Capillary RFIC

Pump10-50 µL/min EG Suppressor

Waste

Injection

Trap Guard Separator

Conductivity Detector

Divert Valve(optional)

Waste

GroundingUnion

ESI-MS/MSMixing Tee

OrganicSolvent

AXP-MS10-50 µL/min

To AssistDesolvation

InstrumentationA Dionex ICS-5000 RFIC system was used in this study, consisting of a SP Single Pump, an eluent generator (EG) module with a Thermo Scientific Dionex EGC-KOH (Capillary) Cartridge, and a DC Detector/Chromatography Compartment featuring a Thermo Scientific™ Dionex™ IC Cube™ with suppressed conductivity detection. The suppressor was operated in external-water mode with DI water regenerant delivered by a Thermo Scientific Dionex AXP-MS Auxiliary Pump at a flow rate of 50 µL/min.

As seen in Figure 1, the eluent of the RFIC system conductivity detector was connected to a divert valve which directs the flow to waste or the MS detector flow path. Organic desolvation solvent was delivered by another Dionex AXP-MS Auxiliary Pump, combined with the chromatographic eluent via a micromixing tee, and passed through a grounding union before entering the MS detector via the optimized capillary ESI interface.

The detailed chromatographic and MS detection conditions are listed with each chromatogram.

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Customizable Interface Parameters• Spray capillary i.d.• ESI probe depth• Proximity of spray tip to MS entrance • ESI voltage• Temperatures (vaporizer and capillary)• Gas �ows (sheath, auxiliary, and ion-sweep gas)

Desolvation Solvent Parameters• Choice of organic desolvation solvent• Flow rate of desolvation solvent

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Customizable Interface Parameters• Spray capillary i.d.• ESI probe depth• Proximity of spray tip to MS entrance • ESI voltage• Temperatures (vaporizer and capillary)• Gas �ows (sheath, auxiliary, and ion-sweep gas)

Desolvation Solvent Parameters• Choice of organic desolvation solvent• Flow rate of desolvation solvent

Figure 2. The Ion Max source interface and optimization parameters.

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Figure 3. Spray capillary i.d. affects sensitivity.

291201 ppm of each analyte, 10 µL full-loop injection. Experiments performed using a Thermo Scienti�c™ MSQ Plus™ Mass Detector (single quad).

34 Gauge Capillary

0.02 1.25 2.50 3.75 5.00 6.25 7.50 9.48

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Fluoride Nitrate

Nitrate

Figure 4. Desolvation solvent improves sensitivity.

The desolvation solvent parameters also need to be optimized for each application. The choice of organic solvent and the flow rate of its introduction were observed to be of particular importance in improving MS detection sensitivity. As seen in Figure 4, more than a 10-fold increase in MS response was achieved at the experimentally determined optimal flow rate of desolvation solvent (acetonitrile in this experiment).

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60%

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120%

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MS Response vs CH3CN Flow Rate(IC Flow at 10 µL/min)

CH3CN Flow Rate (µL/min)

Norm

alize

d Re

spon

se

Endothall Glutarate

• Desolvation solvent signi�cantly improves sensitivity

• Optimum desolvation �ow rate depends on: 1) Analytes 2) Instrumentation

Figure 3 demonstrates the significant effect on MS sensitivity from the spray capillary internal diameter. The top chromatograms were obtained using a 32 gauge (0.235 mm) capillary, and the bottom chromatograms were obtained on a 34 gauge capillary (0.184 mm). With the same injection volume, significantly higher sensitivity can be achieved via the smaller internal diameter ESI capillary.

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Figure 5. Sensitive and selective determination of common anions and organic acids using capillary IC-MS.

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0 1.3 2.5 3.8 5 6.3 7.5 8.8 10 -2.0

18.0

µS

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7.0E4 SIM_06: 149 mz

5.0E5 SIM_05: 97 mz

7.0E4 SIM_04: 97 mz

3.0E5 SIM_03: 62 mz

1.8E4 SIM_02: 39 mz

4.0E4 SIM_01: 35 mz chloride

�uoride

nitrate

phosphate

sulfate

tartrate

Inten

sity

Chromatographic ConditionSystem: Dionex ICS-5000 RFIC systemColumn: Thermo Scienti�c™ Dionex™ IonPac™ AS20 and AG20, 0.4 mmTemp.: 30 °CFlow Rate: 10 µL/minInjection Vol.: 2 µLMobile Phase: 32 mM hydroxide, generated using Dionex EGC-KOH (Capillary) CartridgeSolvent: 10 µL/min acetonitrileDetection: 1st detector: Suppressed Conductivity Thermo Scienti�c™

Dionex™ ACES™ 300 Anion Capillary Electrolytic Suppressor, external water mode 2nd detector: MSQ Plus Mass Spectrometer

Mass Spectrometric ConditionSystem: MSQ PlusInterface: Negative ESINeedle Voltage: 2200 VNebulizer Gas: 60 psiProbe Temp.: 300 °COperating Mode: Selected Ion Monitoring (SIM)Sample: 100 ppb each

Ultratrace-Level Perchlorate in Environmental WaterPerchlorate has been found in various media and is now considered a widespread contaminant in the United States. Perchlorate poses an adverse effect on human health by competitively inhibiting iodide uptake and reducing thyroid hormone production, which is essential for proper protein expression, neuronal differentiation, and other functions.

Figure 6 shows the ultrasensitive quantitation of perchlorate at a 10 parts-per-trillion (ppt, ng/L) level using an online solid-phase extraction (SPE) capillary IC-MS configuration. Using this setup, a 1 mL sample is injected directly onto the online Thermo Scientific™ Dionex™ IonSwift™ MAC-200 Monolith Anion Concentrator Column, and using an MSQ Plus single quadrupole mass spectrometer, is detected using selected ion monitoring (SIM) mode.

EndothallEndothall is an herbicide widely used for both terrestrial and aquatic weeds, including defoliation of cotton, the control of aquatic weeds and algae, and as a desiccating agent for potatoes. Human exposure to endothall in excess of the maximum contamination level (MCL) may cause gastrointes-tinal problems, and therefore is regulated in drinking water by the United States Environmental Protection Agency (EPA) with an MCL of 100 μg/L and by the California EPA with a public health goal (PHG) of 580 μg/L.

ApplicationsCommon Anions and Organic AcidsThe first application using capillary IC-MS demonstrates the confirmation and sensitive quantitation of five commonly seen anions: fluoride, chloride, nitrate, sulfate, and phosphate, and one selected organic acid: tartaric acid. As shown in Figure 5, these analytes can be detected with excellent sensitivity and selectivity. This application takes advantage of the capillary format of the ion exchange column which improves the detection limits with the same injection volume, as well as the enhanced low mass detection capability of the MSQ Plus single quadrupole mass spectrometer for the detection and quantitation of low molecular weight analytes with significantly improved sensitivity.

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Figure 6. Ultratrace-level perchlorate determination using online SPE and capillary IC-MS.

Figure 7 shows the direct analysis of trace-level endothall in water samples. Endothall was separated from seven common anions on a capillary Dionex IonPac AS19 column within 10 min using an electrolytically generated hydroxide gradient at 10 μL/min. The Thermo Scientific™ TSQ Quantum Access™ MS/MS instrument was operated in selected reaction monitoring (SRM) mode, requiring minimal sample cleanup and ensuring highly sensitive (low ppb) and selective quantitation. Isotope labeled glutaric acid (glutaric acid–d6) was used as an internal standard to ensure quantitative accuracy. This application combines the increased mass response of capillary IC with the selectivity and sensitivity of MS/MS to identify the regulated compound endothall.

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Chromatographic ConditionSystem: Dionex ICS-5000 RFIC systemColumn: Dionex IonPac AS20 and AG20, 0.4 mmTemp.: 30 °CFlow Rate: 10 µL/minInjection Vol.: 1 mL on Dionex IonSwift MAC-200 Monolith Anion Concentrator ColumnMobile Phase: Hydroxide, gradient generated using a Dionex EGC-KOH (Capillary) Cartridge Time/min Conc./mM –4.0 20 12 20 12.1 80 17.5 80 17.6 20 20 20Solvent: 10 µL/min acetonitrileDetection: 1st detector: Suppressed conductivity Dionex ACES 300 Anion Capillary Electrolytic Suppressor (external water mode) 2nd detector: MSQ Plus Mass Spectrometer

Mass Spectrometric ConditionSystem: MSQ Plus Mass SpectrometerInterface: Negative ESINeedle Voltage: 2200 VNebulizer Gas: 60 psiProbe Temp.: 300 °COperating Mode: SIMSample: 10 ng/L (ppt)

7.0E3 SIM_01: 99 m/z

2.6E3 SIM_02: 101 mz

0 5 10 15 20 24

40 Conductivity

S/N: 50

S/N: 126

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Figure 7. Quantitation of the herbicide endothall in environmental water samples.

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Chromatographic ConditionSystem: Dionex ICS-5000 RFIC systemColumn: Dionex IonPac AS20 and AG20, 0.4 mmTemp.: 30 °CFlow Rate: 10 µL/minInjection Vol.: 1 mL on Dionex IonSwift MAC-200 Monolith Anion Concentrator ColumnMobile Phase: Hydroxide, gradient generated using a Dionex EGC-KOH (Capillary) Cartridge Time/min Conc./mM –4.0 20 12 20 12.1 80 17.5 80 17.6 20 20 20Solvent: 10 µL/min acetonitrileDetection: 1st detector: Suppressed conductivity Dionex ACES 300 Anion Capillary Electrolytic Suppressor, external water mode 2nd detector: TSQ Quantum Access Mass Spectrometer

System: TSQ Quantum Access MS/MSInterface: Negative ESISpray Voltage: 4000 VSheath Gas: 15 arbitrary unitsAuxiliary Gas: 10 arbitrary unitsCapillary Temp.: 250 °CCollison Gas: Argon at 1.5 m TorrSRM Acquisition: 4.2 to 6 minOperating Mode: SRMSample: Endothall (100 ppb) in seven anion matrix

0 2 4 6 8 10 12 14 16 18 20Minutes

0

50 Suppressed Conductivity

8.16E5

SRM: 185 141

Endothall-Q

1.93E4

SRM: 185 43

Endothall-C

3.31E5

SRM: 137 93

IS: Glutarate-d6

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ConclusionThis study describes the instrumentation of capillary ion chromatography with mass spectrometry, and the importance of optimizing the interface parameters to achieve the best system performance. Analytical solutions developed using these optimized configurations demonstrate successful application to trace level environmental analysis, including common anions and organic acid, perchlorate, and herbicide endothall residue in environmental water samples.