Low-level speciated analysis of Cr(III) and Cr(VI) using LC(IC)-ICP-MS

Significance of the topic

Chromium occurs in two oxidation states with contrasting health impacts: Cr(III) is an essential nutrient, whereas Cr(VI) is a known carcinogen. Its wide industrial use and stringent drinking water regulations—including proposed limits as low as 0.02 µg/L for Cr(VI)—make reliable speciation methods critical for environmental, food and consumer product analysis.

Objectives and overview of the study

This application note presents a robust LC-ICP-MS method using anion exchange chromatography and a helium collision/reaction cell to separate and quantify Cr(III) and Cr(VI) in various water matrices. The goals include demonstrating low detection limits, high recovery in mineralized waters and further optimization for ultra-trace Cr(VI) analysis.

Methodology

Cr(III) is converted into an anionic EDTA complex to enable simultaneous separation with anionic Cr(VI) on a polyhydroxymethacrylate-based anion exchange column. The mobile phase comprises 5 mM EDTA(2Na) and 5 mM NaH2PO4/15 mM Na2SO4 at pH 7.0, delivered at 1.2 mL/min. A large injection volume (100 µL) ensures low detection limits. The ORS3 collision cell operated in helium mode removes ArC and ClO interferences. Dual isotope monitoring (52Cr and 53Cr) provides internal validation.

Used instrumentation

• Agilent 1200 HPLC with binary pump, autosampler, vacuum degasser and PEEK bio-compatibility kit
• Agilent 7700x ICP-MS equipped with ORS3 helium collision cell

Main results and discussion

Detection limits below 200 ng/L for both Cr species were achieved with 100 µL injections. Long-term stability (8 h, n=30) in three mineral waters yielded recoveries of 90–100 % and RSDs <2.5 %. Method modification—larger injection and reduced EDTA—lowered the Cr(VI) detection limit to ~0.008 µg/L, with calibration linearity >0.9995. Analysis of California drinking and river waters revealed Cr(VI) above the proposed 0.02 µg/L threshold.

Benefits and practical applications of the method

The approach offers rapid (~3 min) speciation, excellent sensitivity and reproducibility in complex matrices, internal interference control via helium cell and dual isotopes, and compliance with stringent regulatory limits.

Future trends and potential applications

Advances may include tailored cell gases for further interference removal, on-line preconcentration to push detection limits lower, miniaturized LC-MS interfaces, and adaptation to other redox-sensitive element speciation in environmental and biological samples.

Conclusion

The described LC-ICP-MS method provides a fast, reliable and highly sensitive platform for routine determination of Cr(III) and Cr(VI) across diverse water samples, meeting current and emerging regulatory demands.

Reference

• Mina Tanoshima, Tetsushi Sakai, Craig Jones. Low-level speciated analysis of Cr(III) and Cr(VI) using LC(IC)-ICP-MS. Agilent Technologies Application Note, 2012; Publication 5990-9366EN.