Determination of Oxyhalide Disinfection By-products in Water by Suppressed Anion Chromatography Coupled with Mass Spectrometry

Significance of the Topic

Ensuring the safety of drinking water is a critical public health concern. Disinfection processes using chlorine, chlorine dioxide, sodium hypochlorite or ozone effectively eliminate pathogenic microorganisms but also generate disinfection by-products (DBPs). Among these, oxyhalides such as chlorite, chlorate and bromate pose potential health risks, with bromate recognized as a possible human carcinogen. Regulatory limits, for example the US EPA maximum contaminant level of 10 ppb for bromate, necessitate sensitive, reliable analytical methods for monitoring these compounds in treated water.

Objectives and Overview

This study aimed to develop and validate a robust ion chromatography–mass spectrometry (IC-MS) method for simultaneous quantification of chlorite, chlorate and bromate in drinking water. Key goals included achieving sub-ppb detection limits, high reproducibility and accurate recovery in diverse water matrices without extensive sample preparation or chemical additives.

Methodology and Instrumentation

The analytical platform consisted of a modular Shimadzu ion chromatograph equipped with an electrolytically regenerated suppressor and a Prominence single quadrupole mass spectrometer (LCMS-2020) with an electrospray ionization (ESI) interface operated in negative mode. Conductivity detection monitored the column effluent, while a divert valve directed target oxyhalides to the mass spectrometer. A second pump delivered deionized water through the suppressor regeneration channel to maintain low eluent conductivity and protect the MS from salt buildup.

Main Results and Discussion

• Calibration and Linearity: Six-point calibration curves covered 0.5–100 ppb for chlorite and chlorate and 0.5–25 ppb for bromate. Weighted regression (1/c) yielded correlation coefficients above 0.999 for each isotopic mass.
• Retention and Mass Detection: Chlorite and chlorate eluted at approximately 10.5 and 18.8 minutes, respectively, with characteristic isotopic mass-to-charge (m/z) ratios of 66.9/68.9 for chlorite and 82.9/84.9 for chlorate. Bromate elution occurred at 10.9 minutes with m/z 126.8/128.8.
• Precision and Reproducibility: Seven replicate injections at 0.5, 1 and 10 ppb concentrations showed relative standard deviations below 6.5%, with values under 3% at 10 ppb, demonstrating excellent method precision.
• Recovery in Real Samples: Spiking six different water samples at 10 ppb yielded recoveries between 84.1% and 113.6% for all three oxyhalides, confirming method accuracy in complex matrices.

Benefits and Practical Applications

The developed IC-MS method offers the following advantages:

• Sensitivity: Detection and quantification at concentrations below 0.5 ppb without derivatization.
• Specificity: Mass identification ensures confident compound assignment, even in complex water samples.
• Throughput: Simultaneous analysis of multiple anions with minimal sample handling accelerates routine monitoring workflows.

Future Trends and Potential Applications

Emerging trends in water quality analysis include coupling high-resolution mass spectrometry with ion chromatography for non-target screening of novel DBPs. Advances in inline sample preconcentration and improved suppressor technologies will further lower detection limits. Integration of automated data processing and cloud-based reporting can streamline compliance monitoring and support real-time decision-making.

Conclusion

A sensitive, simple and robust IC-MS protocol was established for simultaneous quantification of chlorite, chlorate and bromate in drinking and bottled water. Using a novel electrolytic suppressor and single quadrupole MS, the method achieves sub-ppb detection, high reproducibility and accurate recoveries without laborious sample preparation. This approach supports efficient regulatory compliance and enhances water quality assurance.

References

• Guo H, Marfil-Vega R. Determination of Oxyhalide Disinfection By-products in Water by Suppressed Anion Chromatography Coupled with Mass Spectrometry. Shimadzu Scientific Instruments, Inc.