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

Importance of the Topic

Ensuring the safety of drinking water is critical for public health. While disinfection using chlorine-based agents or ozone effectively inactivates pathogens, it also leads to formation of disinfection by-products (DBPs) such as chlorite, chlorate and bromate. These oxyhalides present potential health risks, with bromate classified as a possible human carcinogen and regulated at a maximum contaminant level of 10 ppb by the US EPA.

Objectives and Study Overview

This study aimed to develop a robust and sensitive analytical method for simultaneous quantification of chlorite, chlorate and bromate in drinking water. The approach integrates suppressed anion chromatography with a novel electrolytically regenerated suppressor and single quadrupole mass spectrometry employing electrospray ionization in negative mode. Conductivity detection directs target analytes to the mass spectrometer via a divert valve, enabling selective monitoring.

Instrumentation Used

• A modular Shimadzu Prominence IC system featuring an electrolytically regenerated suppressor
• Two pumps: one for eluent delivery to the chromatographic column and another for suppressor regeneration at 1.2 mL/min
• Conductivity detector to monitor column effluent and control valve position
• Shimadzu LCMS-2020 single quadrupole mass spectrometer with an ESI interface operating in negative ion mode
• Divert valve to route only oxyhalide peaks to the MS, protecting the detector from excess salts

Methodology

Water samples were injected into the IC system with an ion-exchange column. The eluent was suppressed via continuous electrochemical generation of hydronium ions, converting salts into their corresponding acids and lowering background conductivity. A conductivity detector tracked eluent composition, triggering a valve to direct analyte-rich fractions to the MS for selected ion monitoring of characteristic isotopic masses. Calibration curves were prepared over 0.5–100 ppb for chlorite and chlorate, and 0.5–25 ppb for bromate, using 1/x weighting.

Main Results and Discussion

Linear calibration (r2>0.999) and accuracy between 82–120 % were achieved for all three analytes at each isotopic mass. Retention times were 10.5 min for chlorite, 10.9 min for bromate and 18.8 min for chlorate, with expected isotopic ratios observed. Method precision was excellent, with RSDs below 3 % at 1 ppb and 10 ppb levels and below 6.5 % at 0.5 ppb. Recovery tests in six drinking water matrices spiked at 10 ppb yielded recoveries of 84.1–113.6 %, demonstrating minimal matrix effects and high recovery.

Benefits and Practical Applications

• No arduous sample preparation or post-column derivatization required
• Simultaneous detection of multiple oxyhalides in a single run
• Low detection limits below regulatory thresholds
• High specificity and confidence through mass-based identification
• Suitable for routine monitoring in QA/QC laboratories and water utilities

Future Trends and Opportunities

• Integration with high-resolution mass spectrometry for enhanced selectivity
• Automation and online coupling for real-time water quality monitoring
• Miniaturized and portable IC-MS systems for field deployment
• Expansion to additional DBPs and emerging contaminants
• Implementation in large-scale water treatment facilities for continuous compliance

Conclusion

The newly developed IC-MS approach provides a fast, sensitive and reliable means to quantify chlorite, chlorate and bromate in drinking water without complex sample handling. Its compatibility with routine laboratory workflows and compliance with regulatory requirements makes it a valuable tool for safeguarding water quality.