Fast determination of oxyhalides and bromide in drinking water using a compact ion chromatography system coupled with a single quadrupole mass spectrometer

Significance of the topic

The formation of oxyhalides and bromate during chemical disinfection of drinking water raises health concerns due to their potential carcinogenicity. Regulatory agencies worldwide limit bromate concentrations to 10 µg/L or lower, necessitating analytical methods that deliver rapid, precise, and sensitive measurements.

Study objectives and overview

This work describes development of a 15-minute isocratic ion chromatography method coupled with single quadrupole mass spectrometry (IC-MS) for simultaneous determination of chlorite, bromate, chlorate, and bromide in drinking water, aiming to improve sensitivity and selectivity compared to conventional conductivity detection.

Methodology and Instrumentation

• Chromatography was performed on a Thermo Scientific Integrion RFIC system using an IonPac AG19 guard column and AS19 analytical column with 40 mM KOH eluent at 0.25 mL/min.
• An AERS 500e suppressor in external water mode and suppressed conductivity detection monitored eluent output.
• Mass spectrometric detection used an ISQ EC single quadrupole with heated electrospray ionization (negative mode) and selective ion monitoring corresponding to each anion.
• Standards were preserved with ethylenediamine, and an isotopically labeled bromate-18O internal standard compensated for matrix effects and signal variation.

Key Results and Discussion

• Complete baseline separation of target anions within 15 minutes using isocratic elution.
• Limits of detection (S/N=3) and method detection limits (MDLs) ranged from 0.025 to 0.05 µg/L in DI water and 0.029 to 0.036 µg/L in high-ionic strength matrices.
• Calibration across 0.25–10 µg/L showed excellent linearity (r² > 0.999) with internal standard normalization.
• Recovery in bottled and tap water samples ranged from 75% to 104%, complying with EPA Method 300.1 requirements.
• Instrument precision over three days achieved retention time relative standard deviation (RSD) <0.4% and peak area RSD <2%.

Benefits and Practical Applications

• Short analysis time and enhanced sensitivity relative to gradient IC-CD methods.
• Positive identification via mass spectrometry reduces interference in complex samples.
• Elimination of make-up solvents simplifies system configuration and maintenance.

Future Trends and Potential Applications

• Adapting the IC-MS platform to additional regulated inorganic anions and emerging disinfection byproducts.
• Integration with high-resolution MS for non-targeted screening in environmental monitoring.
• Automation for real-time water quality assessment in treatment plants.

Conclusion

The presented isocratic IC-MS method enables rapid, robust, and highly sensitive monitoring of oxyhalides and bromide at regulatory levels, supporting compliance and safeguarding drinking water quality.

References

1. U.S. EPA Method 300.1 Part B (1997).
2. World Health Organization, Background Document for Bromate in Drinking Water (2005).
3. Dionex Integrion and IonPac AS19-4µm column manuals.
4. Thermo Fisher Scientific Application Note 72866.
5. ICH Q2B Validation of Analytical Procedures (1996).