Ion Chromatography (IC) ICP-MS for Chromium Speciation in Natural Samples

Significance of the Topic

Chromium exists in two oxidation states in natural waters: Cr(III), an essential micronutrient, and Cr(VI), a potent mutagen and carcinogen. Total chromium measurements alone cannot assess toxicity risk, so reliable speciation to distinguish and quantify both forms is critical for environmental monitoring, drinking water safety and regulatory compliance.

Aims and Study Overview

This application note describes the development of a streamlined, robust method to separate and quantify Cr(III) and Cr(VI) in complex water matrices. It couples ion chromatography (IC) with an Octopole Reaction Cell ICP-MS to achieve rapid, interference-free speciation at trace levels.

Methodology and Instrumentation

• Sample stabilization: Incubation at 40 °C for 3 h with EDTA (5–15 mM) at pH 7 to complex Cr(III).
• Chromatography: Agilent G3268A anion-exchange column (30 mm×4.6 mm), mobile phase 5 mM Na2EDTA, pH 7, flow 1.2 mL/min, ambient temperature, injection volumes 50–500 µL.
• IC delivery: Metrohm 818 IC Pump with Agilent 7500ce Integrated Sample Introduction System (ISIS) for precise sample loop switching.
• Detection: Agilent 7500ce ICP-MS in H2 reaction gas mode at mass 52 to remove ArC and ClOH interferences.

Main Results and Discussion

The method achieves baseline separation of Cr(III) and Cr(VI) in about 3 minutes. Detection limits on a 100 µL injection are <20 ng/L for each species, improving to ~13 ng/L (Cr(III)) and ~16 ng/L (Cr(VI)) with a 500 µL injection. Calibration curves from 0.05 to 1.0 µg/L are linear with excellent sensitivity. Retention time and peak area stability over multiple injections show RSDs below 3%. Spike recoveries in two mineral waters (one with ~100 mg/L calcium, the other >450 mg/L calcium and >1000 mg/L sulfate) ranged from 95% to 105%, demonstrating accurate quantification in high-matrix samples.

Benefits and Practical Applications

• Fast and cost-effective speciation in a single analysis.
• High sensitivity and low detection limits suitable for regulatory monitoring (e.g., 0.1 µg/L Cr(VI) standards).
• Robust performance in hard and mineralized waters due to optimized EDTA stabilization.
• Interference removal via reaction cell enables accurate trace quantification.

Future Trends and Potential Applications

Further developments may include expansion to other redox-sensitive elements, integration with on-line preconcentration, miniaturized or field-deployable systems, automation for high-throughput monitoring and exploration of greener reagents and lower flow rates to reduce solvent consumption.

Conclusion

This optimized IC-ICP-MS method provides a rapid, sensitive and reliable approach for chromium speciation in natural and high-matrix water samples. It meets stringent detection requirements, ensures species stability and offers strong applicability for environmental and drinking water quality laboratories.

Reference

• Agilent Technologies, Application Note 5989-2481EN, April 2005.