Determination of Common Anions and Organic Acids Using Ion Chromatography- Mass Spectrometry

Significance of the Topic

The integration of mass spectrometry with ion chromatography provides enhanced sensitivity, selectivity and structural confirmation for trace-level anion and organic acid analysis. This capability is critical in environmental, food and water quality monitoring where accurate quantification and identity confirmation at parts-per-billion levels drive regulatory compliance and safeguard public health.

Objectives and Study Overview

This study demonstrates an IC–MS method using a single‐quadrupole mass spectrometer to quantify five common inorganic anions (fluoride, chloride, nitrate, sulfate, phosphate) and three organic acids (pyruvate, α-ketoglutarate, tartrate). Key performance metrics—calibration range, reproducibility and method detection limits—were established and the method was applied to a real bottled water sample.

Methodology and Instrumentation

The separation was performed on a Dionex ICS-2000 RFIC™ system with an IonPac AS20 analytical column (2.1 × 250 mm) and AG20 guard (2.1 × 50 mm), featuring a CR-ATC trap column. Eluent was 28 mM KOH generated by EGC II, delivered at 0.25 mL/min. A suppressed conductivity detector (external water, 0.50 mL/min) was coupled to a Thermo Scientific MSQ Plus™ single‐quadrupole mass spectrometer. Electrospray ionization in negative SIM mode monitored characteristic adducts (e.g., [F(HF)]⁻ at m/z 39.1). MS source conditions (probe temperature 450 °C, nitrogen nebulizer at 85 psi, needle voltage 1.5 kV) were optimized by response surface methodology.

Main Results and Discussion

Calibration was linear or polynomial over 2–1000 ppb (100–1000 ppb for fluoride), with correlation coefficients >0.98. Method detection limits ranged from 2.5 ppb (nitrate) to 29.4 ppb (fluoride). Chromatographically separated sulfate and phosphate peaks at m/z 97 enabled accurate quantitation despite identical mass. In bottled water, chloride (713 ppb), sulfate (496 ppb), nitrate (143 ppb) and phosphate (181 ppb) were detected without sample preparation.

Benefits and Practical Applications

• High specificity from SIM detection reduces interferences.
• Low ppb detection without preconcentration or derivatization.
• Rapid, direct analysis of environmental and drinking water samples.

Future Trends and Potential Applications

Advances in high‐resolution MS and integrated software workflows will further improve identification confidence and throughput. Expanding IC–MS to new anion classes, coupling with automated sample preparation and exploring miniaturized systems can broaden field and on-site testing capabilities.

Conclusion

The described IC–MS approach delivers robust, sensitive quantification of key anions and organic acids in complex matrices. Its simplicity, low detection limits and structural confirmation make it an attractive alternative to traditional conductivity detection for trace-level water analysis.

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