Chromium Speciation of Drinking Waters by IC-ICP-MS

Importance of the Topic

Chromium speciation is critical due to the contrasting roles of Cr(III) as a micronutrient and Cr(VI) as a carcinogen. Regulatory limits for total chromium in drinking water necessitate methods that can reliably distinguish these species at sub-ppb levels to ensure public health and compliance.

Objectives and Study Overview

This work evaluates a hyphenated technique combining Shimadzu Prominence Ion Chromatography with the Shimadzu ICPMS-2030 to achieve rapid, direct analysis of Cr(III) and Cr(VI) in drinking water. The study benchmarks separation efficiency, detection limits, accuracy, and long-term stability without sample pretreatment.

Methodology

Water samples (tap and well) were analyzed directly or after spiking with Cr(III) and Cr(VI) standards. Calibration standards ranged from 2 to 10 µg/L. A Shodex VC-50 2D column with 9 mM nitric acid mobile phase (isocratic) at 0.3 mL/min and 50 °C provided chromatographic separation in under 10 min. Injection volume was 20 µL. No complexing agents were used, simplifying preparation and minimizing contamination risk.

Instrumentation

• Shimadzu Prominence IC: inert flow path controller, online degasser, LC-20Ai pump, SIL-20AC autosampler, CTO-40C column oven.
• Shimadzu ICPMS-2030: 1.2 kW RF power, helium collision cell, sampling depth 5 mm, main isotope 52 m/z.

Key Results and Discussion

• Baseline separation of Cr(III) and Cr(VI) within 10 min with R² > 0.9999 for both species.
• Detection limits of 0.20 µg/L (Cr(III)) and 0.35 µg/L (Cr(VI)), two orders of magnitude below the EPA MCL.
• Recovery of spiked samples within ±5%, demonstrating accuracy in various matrices.
• Retention time RSD < 1.4% and peak area RSD < 2.6% over 7.2 h, confirming method stability.

Benefits and Practical Applications

This approach eliminates lengthy derivatization steps and avoids complexing agents, reducing analysis time and contamination risk. The high sensitivity and precision make it suitable for routine monitoring of drinking water, environmental testing, and QA/QC laboratories.

Future Trends and Potential Applications

Increasing injection volumes or employing higher-capacity columns could further lower detection limits. The platform may be extended to multi-element speciation, real-time monitoring, or coupled with automated sample preparation for high-throughput workflows.

Conclusion

The described IC-ICP-MS method provides a fast, sensitive, and robust solution for chromium speciation in drinking waters. Its minimal sample prep and strong analytical performance support its adoption for regulatory and research applications.

References

• Practical Guide to ICP-MS, Robert Thomas, Marcel Dekker, Inc.