Trace Level Determination of Bromate in Ozonated Drinking Water Using Ion Chromatography

Significance of the Topic

Ozonation has become a widely adopted alternative to chlorination in water treatment because it generates fewer regulated byproducts. However, the oxidation of bromide to bromate during ozonation poses a health concern, since bromate is classified as a potential carcinogen at microgram-per-liter levels. Accurate trace-level detection of bromate in drinking water is critical to support process optimization, regulatory compliance, and public safety.

Objectives and Study Overview

This study presents a modified ion chromatography method with sample preconcentration to lower the method detection limit (MDL) for bromate in ozonated drinking water. The aim was to reduce the typical MDL of about 7.3 µg/L achieved by direct injection to below 1 µg/L, enabling reliable quantification at concentrations relevant to U.S. EPA recommendations (< 10 µg/L) and ongoing health risk assessments.

Methodology and Instrumentation

Water samples were first sparged to remove dissolved ozone and chlorine dioxide, then preserved with ethylenediamine to block hypobromite conversion. A two-step chemical pretreatment followed:

• Addition of magnesium chloride and sodium carbonate to promote consistent sulfate removal on a barium-form cation cartridge.
• Sequential passage through OnGuard-Ag and OnGuard-H cartridges to eliminate chloride (as silver chloride) and residual carbonate (converted to carbonic acid and sparged off), improving selectivity and preventing cartridge fouling.

Preconcentration exploited a Thermo Scientific Dionex TAC-LP1 concentrator column. A weak borate eluent first loads retained anions onto the analytical columns (IonPac AG9 and AS9-SC), then a stronger borate flush ensures complete elution before the next injection. Sample volumes of up to 5 mL yield significant enrichment compared to direct injection.

Key Results and Discussion

The enhanced method achieved MDLs for bromate down to 0.3 µg/L in raw water matrices and around 0.9–1.7 µg/L for spiked raw samples. In ozonated water, MDLs ranged up to 5.1 µg/L due to elevated background ions. Consistent sulfate displacement required ≥ 120 mg/L magnesium. The pretreatment cartridges effectively eliminated matrix interferences, enabling clear bromate resolution from high chloride, sulfate, and carbonate backgrounds. Chromatographic stability was maintained by installing a MetPac CC-1 metal-trap column to protect against silver leaching and other metal fouling.

Benefits and Practical Applications

The preconcentration suppressed-conductivity IC method provides:

• Improved sensitivity for regulatory and research monitoring of bromate at sub-µg/L levels.
• Robust performance in complex drinking water matrices with high anion content.
• A framework adaptable to ASTM guidance for oxyhalide determination.

This approach supports water utilities and laboratories in process development, QA/QC, and compliance verification of ozonation systems.

Future Trends and Opportunities

Advances may include on-line or automated sample preparation, coupling with mass spectrometry for compound identification, miniaturized concentrator modules, and development of high-capacity alternative sorbents. As regulatory limits tighten, further lowering detection limits and extending the method to other disinfection byproducts will be valuable. Integration with remote monitoring and data analytics could enhance real-time water quality control.

Conclusion

The described suppressed IC method with sample preconcentration significantly lowers the MDL for bromate, offering reliable trace analysis in ozonated drinking water. Its robustness against matrix effects, alignment with ASTM practices, and sub-µg/L sensitivity make it an effective tool for ensuring water safety and guiding disinfection strategies.

References

1. Haag WR, Hoigné J. Environmental Science and Technology. 1983;17:261.
2. Hautman DP, Bolyard MJ. Journal of Chromatography. 1991;602:7.
3. American Society for Testing and Materials. Proposed ASTM Method Determination of Oxyhalides and Bromide in Water by Chemically Suppressed Ion Chromatography, under review by ASTM D-19 Committee on Water.
4. Thermo Fisher Scientific. Application Note 101: Trace Level Determination of Bromate in Ozonated Drinking Water Using Ion Chromatography.