Ion Chromatographic Determination of Oxyhalides and Bromide at Trace Level Concentrations in Drinking Water Using Direct Injection

Importance of the Topic

The formation of disinfection byproducts (DBPs) such as chlorite, chlorate and bromate during water treatment poses significant health risks. Regulatory programs like the U.S. EPA Information Collection Rule (ICR) mandate sensitive, reliable monitoring of oxyhalides and bromide at trace levels in drinking water. Accurate quantification ensures public safety and compliance with EPA Method 300.0 requirements.

Objectives and Overview of the Study

This work presents an ion chromatographic (IC) method employing direct injection and an IonPac AS9-HC column to separate and quantify trace concentrations of chlorite, chlorate, bromate and bromide in the presence of high levels of common anions. The goal was to achieve low detection limits without cartridge pretreatment and to demonstrate method linearity, precision and robustness under typical drinking water matrices.

Instrumentation Used

• Dionex DX-500 IC system with GP40 gradient pump, CD20 suppressed conductivity detector and AS40 autosampler.
• LC20 enclosure featuring a rear-loading injection valve in external water suppression mode.
• IonPac AS9-HC analytical column (4×250 mm) and AG9-HC guard column (4×50 mm).
• PeakNet chromatography workstation for data acquisition.

Methodology

An isocratic eluent of 9 mM sodium carbonate was prepared by diluting 18 mL of 0.5 M carbonate concentrate to 1 L. Samples (200 µL injection) were sparged to remove reactive gases and preserved with ethylenediamine to prevent analyte conversion. The separation ran at 1.0 mL/min over 25 minutes with suppressed conductivity detection (ASRS™-II, external water mode). Working standards were prepared daily for analyte levels below 100 µg/L.

Main Results and Discussion

Baseline separation of oxyhalides and bromide from fluoride, chloride, nitrite, nitrate, phosphate and sulfate was consistently achieved. Key performance metrics in simulated drinking water (50 mg/L chloride, 150 mg/L bicarbonate, 50 mg/L sulfate) included:

• Method detection limits (MDLs): bromate 1.7 µg/L, chlorite 2.4 µg/L, bromide 1.8 µg/L, chlorate 1.1 µg/L.
• Linearity ranges: bromate 5–40 µg/L (r²=0.9998), chlorite/chlorate/bromide 20–500 µg/L (r²>0.999).
• System background conductivity stabilized at 20–24 µS with noise of 6–10 nS after ~5 hours of equilibration.
• Maximum injection volume for trace analysis without peak coelution: 500 µL.

Benefits and Practical Applications

The direct-injection IC approach eliminates the need for pretreatment cartridges, simplifying routine monitoring of DBP precursor ions in water utilities. High resolution between bromate and chloride in high-chloride samples enables reliable compliance testing under ICR guidelines using standard instrumentation.

Future Trends and Potential Uses

Advances may include coupling to mass spectrometry for enhanced specificity, further miniaturization of IC systems for field deployment and development of novel stationary phases to extend linear ranges and reduce equilibration times. Automated preservation strategies and on-line sample preparation modules could improve throughput.

Conclusion

The described IonPac AS9-HC method delivers robust, sensitive detection of oxyhalides and bromide in drinking water, meeting or exceeding EPA ICR requirements. Its direct-injection format and straightforward eluent system facilitate easy implementation in environmental and regulatory laboratories.

References

1. Federal Register 1996, 61(94), 24354.
2. U.S. Environmental Protection Agency. Method 300.0: The Determination of Inorganic Anions in Water by Ion Chromatography, August 1993.