Determination of Chlorite, Bromate, Bromide, and Chlorate in Drinking Water by Ion Chromatography with an On-Line-Generated Postcolumn Reagent for Sub-μg/L Bromate Analysis

Importance of the Topic

Safe drinking water requires effective disinfection but common oxidants can form harmful oxyhalide by-products such as chlorite, chlorate and bromate. Monitoring these anions at low-µg/L levels is critical to comply with WHO and EPA regulations and to protect public health.

Objectives and Overview of the Study

This application note presents an improved ion chromatography method equivalent to EPA Method 326.0 for simultaneous determination of chlorite, chlorate, bromide and bromate. Key aims included enhancing bromate sensitivity below 1 µg/L and streamlining analysis of all relevant oxyhalide anions in a single run.

Methodology and Instrumentation

The separation is performed on a Thermo Scientific Dionex IonPac AS9-HC column guarded by an AG9-HC cartridge with 9 mM sodium carbonate eluent at 1.3 mL/min and 30 °C. Suppressed conductivity detection (Anion Atlas electrolytic suppressor in external water mode) quantifies chlorite, chlorate and bromide. Bromate is detected by postcolumn reaction with on-line-generated hydroiodic acid from KI in a PC10 delivery module, heated at 80 °C in a PCH-2 reactor coil, forming triiodide detected at 352 nm by UV absorbance. Samples are preserved with ethylenediamine, treated with ferrous sulfate to remove chlorite when needed, filtered and injected with a 225 µL loop on a Dionex AS50 autosampler.

Results and Discussion

Chromatograms show baseline resolution of all four anions with dual detection. Calibration was linear from 5–1000 µg/L (r²>0.999) for conductivity and 0.5–15 µg/L for UV bromate (MDL 0.06 µg/L). Recoveries in drinking water and high-ionic-strength matrices ranged 97–114% for chlorite, chlorate, bromide and 98–107% for bromate. Bottled and treated waters demonstrated reliable quantification. Chlorite interference was effectively removed by ferrous reduction and ion exchange, enabling accurate low-µg/L bromate determination.

Benefits and Practical Applications

• Simultaneous determination of key oxyhalides and bromide in one analysis
• Sub-µg/L quantification of bromate using PCR-UV without compromising conductivity detection of other anions
• On-line reagent generation improves safety and reagent stability
• Compliance monitoring under EPA Stage 1 D/DBP requirements and anticipated Stage 2 rules

Future Trends and Opportunities

Advances in postcolumn chemistries and detector technologies may further lower detection limits and expand analyte scope. Coupling with mass spectrometry could enable identification of emerging disinfection by-products. Miniaturized flow systems and on-site sensors offer potential for real-time monitoring. Method optimization for other regulated ions and integration into automated QA/QC workflows is anticipated.

Conclusion

This enhanced IC method with on-line-generated postcolumn reagent provides a robust, sensitive and versatile platform for monitoring chlorite, chlorate, bromide and bromate in drinking water. It meets regulatory requirements, simplifies workflow and ensures reliable trace-level detection for water quality management.

Instrumentation Used

• Dionex DX-600 IC system (GP50 pump, ED50A conductivity detector, AD25 UV/Vis detector, AS50 autosampler)
• IonPac AG9-HC guard and AS9-HC analytical columns
• PC10 pneumatic postcolumn reagent delivery module
• AMMS 300 Anion MicroMembrane suppressor
• PCH-2 reaction heater and knitted reaction coil

References

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