Determination of Chlorite, Chlorate and Bromate in Water by Suppressed Anion Chromatography Coupled with Mass Spectrometry

Importance of Topic

Disinfection of drinking water with chlorine, chlorine dioxide, sodium hypochlorite, or ozone is essential for eliminating pathogens but also generates oxyhalide disinfection byproducts (DBPs) such as chlorite, chlorate, and bromate. These DBPs pose potential health risks, with bromate identified as a possible human carcinogen, prompting regulatory limits (EPA MCL of 10 ppb for bromate).

Objectives and Study Overview

This work aimed to develop a sensitive, reliable ion chromatography–mass spectrometry (IC-MS) method for simultaneous determination of chlorite, chlorate, and bromate in drinking water at sub-ppb levels. The approach integrates a novel electrolytically regenerated suppressor within a modular IC system and a single-quadrupole mass spectrometer.

Methodology and Instrumentation

The method couples suppressed anion chromatography with electrospray ionization mass spectrometry (ESI-MS) in negative mode. Key components and steps include:

• Shimadzu Prominence IC system with built-in electrolytic suppressor for continuous regeneration and conductivity reduction
• LCMS-2020 single-quadrupole mass spectrometer operating in negative-ion SIM mode targeting characteristic isotopic masses
• Conductivity detector to monitor column effluent and a divert valve to direct only the oxyhalides of interest to the MS
• Quantitative calibration using six-point curves with 1/x weighting across 0.5–100 ppb (chlorite, chlorate) and 0.5–25 ppb (bromate)

Main Results and Discussion

All three oxyhalides exhibited strong linearity (r2 > 0.999). Retention times were approximately 10.5 min for chlorite, 18.8 min for chlorate, and 10.9 min for bromate. Precision testing (seven replicates) yielded RSDs below 3% at 1 ppb and 10 ppb, and under 6.5% at 0.5 ppb. Recovery experiments in six diverse water samples spiked at 10 ppb demonstrated recoveries between 84.1% and 113.6%, confirming method accuracy and robustness.

Benefits and Practical Applications

This IC-MS protocol allows simultaneous, low-level detection of key oxyhalide DBPs without laborious sample preparation or chemical additives. Mass spectrometric identification enhances specificity and confidence, making the technique suitable for regulatory compliance monitoring, industrial QA/QC, and research in complex water matrices.

Future Trends and Opportunities

Potential developments include integration with high-resolution MS for improved selectivity, online automated monitoring platforms for real-time water quality surveillance, expansion to additional emerging anionic contaminants, and miniaturized field-deployable systems for decentralized analysis.

Conclusion

A streamlined and sensitive IC-MS method utilizing an electrolytically regenerated suppressor and single-quadrupole MS achieves sub-ppb quantification of chlorite, chlorate, and bromate with excellent precision and accuracy, providing a powerful tool for comprehensive DBP monitoring in drinking water.

Reference

US EPA. National Primary Drinking Water Regulations: Bromate Maximum Contaminant Level of 10 ppb.