Determination of Trace Concentrations of Oxyhalides and Bromide in Municipal and Bottled Waters Using a Hydroxide- Selective Column with a Reagent-Free™ Ion Chromatography System

Significance of the Topic

The formation of inorganic oxyhalide byproducts such as chlorite, chlorate and bromate during drinking water disinfection poses health risks and is subject to strict regulatory limits. Sensitive, reliable and high-throughput analysis of these anions at low microgram-per-liter levels is essential for municipal and bottled water quality control and regulatory compliance.

Study Objectives and Overview

This work aimed to develop and validate a reagent-free ion chromatography method using a hydroxide-selective column for simultaneous determination of trace chlorite, chlorate, bromate and bromide in treated drinking water and bottled water. Key goals included improving detection limits, enhancing selectivity against high chloride backgrounds and simplifying eluent preparation through electrolytic generation of potassium hydroxide.

Methodology and Instrumentation

• System: Thermo Scientific Dionex ICS-2000 Reagent-Free IC equipped with an EluGen™ EGC II KOH cartridge and a CR-ATC continuously regenerated anion trap column
• Column: Dionex IonPac AG19 guard (4×50 mm) and IonPac AS19 analytical (4×250 mm) with hyperbranched anion-exchange resin tailored for hydroxide eluents
• Eluent: Gradient from 10 to 45 mM KOH generated electrolytically; recycle-mode ASRS™ ULTRA II suppressor for conductivity detection
• Injection volume: 250 µL (500 µL tested but prone to overload for high-ionic-strength samples)
• Flow rate and temperature: 1.0 mL/min at 30 °C
• Preservation: Ethylenediamine addition to stabilize chlorite and prevent bromate formation

Main Results and Discussion

• Detection limits: Method detection limit for bromate of 0.34 µg/L in simulated drinking water, approximately 70% lower than carbonate-based methods
• Linearity and precision: Calibration linear over relevant ranges (1–40 µg/L for bromate, 20–500 µg/L for other oxyhalides) with r²>0.999; retention time RSD<0.03% and peak area RSD<1.1%
• Chloride tolerance: Bromate recovery remained >75% in samples containing up to 150 ppm chloride; combined chloride and sulfate up to 120 ppm each maintained acceptable recoveries
• Recovery in real samples: Single-operator spike recoveries of 75–125% for municipal tap, surface, well and bottled water; one well water sample revealed unexpected background bromate likely from local contamination
• Bottled water survey: Several brands showed bromate at or near the 10 µg/L maximum contaminant level, highlighting the need for routine monitoring

Benefits and Practical Applications

The combination of a high-capacity, hydroxide-selective column and electrolytic eluent generation offers:

• Enhanced sensitivity and lower background noise compared to carbonate eluents
• Elimination of manual eluent preparation and associated contamination risks
• Robust peak resolution between bromate and large chloride matrices
• Automated, high-throughput compliance testing for public water systems and bottled water manufacturers

Future Trends and Applications

Advances likely to extend this approach include coupling with mass spectrometric detectors for ultra-trace analysis, further miniaturization of IC systems for field monitoring and development of tailored columns for additional emerging contaminants. Integration with online sampling and direct-injection modules will support real-time water quality surveillance.

Conclusion

A reagent-free IC method using the Dionex IonPac AS19 column and electrolytically generated hydroxide eluent provides a powerful tool for low-µg/L quantification of oxyhalide disinfection byproducts and bromide in drinking and bottled waters. The technique meets regulatory requirements, simplifies operation and enhances laboratory throughput.

References

• U.S. EPA Method 300.1: Determination of Inorganic Anions by IC, 1997
• World Health Organization. Disinfectants and Disinfection By-Products, 2000
• EU Directive 98/83/EC on the Quality of Water Intended for Human Consumption, 1998
• Dionex IonPac AS19 Anion-Exchange Column Data Sheet