Determination of Oxyhalides in Water Using Suppressed Anion Chromatography Coupled with Single Quadrupole MS

Significance of the Topic

Drinking water disinfection generates byproducts such as chlorite, chlorate and bromate, which pose health risks including carcinogenicity. Regulatory limits (e.g., EPA maximum contaminant level of 10 ppb for bromate) drive the need for analytical methods capable of trace-level detection in complex matrices. High sensitivity, specificity and operational simplicity are essential for routine monitoring and regulatory compliance.

Study Objectives and Overview

This work aimed to develop and validate a sensitive ion chromatography–mass spectrometry (IC-MS) method for simultaneous determination of chlorite, chlorate and bromate in drinking water. A modular Shimadzu IC system with a novel electrolytically regenerated suppressor was coupled to a single quadrupole LCMS-2020. Dual detection—suppressed conductivity and electrospray-MS in negative mode with selective ion monitoring—was implemented to enhance selectivity and sensitivity.

Methodology and Instrumentation

Reagents and Sample Preparation:

• Degassed deionized water (≥18 MΩ·cm)
• Eluent: 5.4 mM Na₂CO₃ prepared from 0.18 M stock
• Standards: 1000 ppm solutions of chlorite, chlorate, bromate in water
• Water samples: bottled, tap, dispenser, and well water, filtered through 0.45 μm PES and stored at 4 °C

Instrumentation:

• Shimadzu modular IC: CBM-40 controller, DGU-403 degasser, LC-20Ai pump, SIL-20AC autosampler, CTO-40S oven, CDD-10Avp conductivity detector, ICDS-40A suppressor
• Shimadzu LCMS-2020 single quadrupole MS with ESI (negative mode)
• LabSolutions CDS v5.97 for data acquisition and processing

Chromatographic and MS Conditions:

• Column: Shodex IC SI-52E (4×250 mm) with guard SI-90G
• Eluent flow: 0.5 mL/min, column temperature 50 °C, injection 300 µL
• Suppressor: electrolytic regeneration at 180 mA with 1.2 mL/min water
• MS parameters: interface 350 °C, heat block 500 °C, nebulizing gas 1.5 L/min, drying gas 15 L/min, interface voltage –5 kV
• SIM masses: m/z 66.9/68.9 (chlorite), 82.9/84.9 (chlorate), 126.8/128.8 (bromate)

Key Results and Discussion

Separation and Detection:

• Chlorite and chlorate eluted at ~10.5 min and 18.8 min; bromate at ~10.9 min
• Signal directed to MS via divert valve, reducing background conductivity and protecting MS

Analytical Performance:

• Calibration linear from 0.5–100 ppb for chlorite/chlorate and 0.5–25 ppb for bromate (r²>0.999)
• Method detection limits (MDLs): 0.06–0.10 ppb across isotopes
• Precision (RSD): <3% at 1 and 10 ppb; ≤6.5% at 0.5 ppb

Water Sample Analysis and Recovery:

• Native levels of oxyhalides were below detection or low in all samples
• Spike recoveries at 10 ppb ranged from 84.1% to 113.6%

These results confirm robust performance, high sensitivity and reproducibility without extensive sample preparation.

Benefits and Practical Applications

• Simultaneous quantification of three oxyhalides at sub-ppb levels
• No need for post-column reagents or complex derivatization
• Mass-based identification enhances selectivity in complex matrices
• Minimized analytical errors and increased laboratory throughput

Future Trends and Applications

• Integration with high-resolution MS for broader anion screening
• Two-dimensional chromatography to resolve coeluting interferences
• Automated sample handling and online monitoring for real-time water quality assessment
• Application to other regulated disinfection byproducts and environmental matrices

Conclusion

The developed IC-MS method using a regenerated suppressor and single quadrupole MS provides high sensitivity, specificity and reproducibility for trace analysis of chlorite, chlorate and bromate in drinking water. It surpasses traditional suppressed conductivity detection in both detection limits and confidence of identification, offering an efficient alternative for routine monitoring and regulatory compliance.

References

1. EPA Method 300.1: Determination of inorganic anions in drinking water by ion chromatography, Revision 1.0.
2. Shimadzu Application Note HPLC-022: Determination of 10 anions in EPA Method 300.1 using Shimadzu high-resolution ion chromatography.