Determination of chromium species using ion chromatography coupled to inductively coupled plasma mass spectrometry

Importance of the Topic

Chromium naturally occurs in the environment in two main oxidation states, Cr(III) and Cr(VI), with very different toxicological and nutritional profiles. While Cr(III) is an essential trace element that supports glucose and lipid metabolism, Cr(VI) is a recognized carcinogen that poses significant health risks. Monitoring the individual species in drinking water is therefore critical to assess exposure hazards and ensure regulatory compliance.

Study Objectives and Overview

This application note describes a targeted approach for separating and quantifying Cr(III) and Cr(VI) in tap water samples using ion chromatography (IC) coupled directly to inductively coupled plasma mass spectrometry (ICP-MS). The goals were to achieve a rapid, robust speciation analysis with low detection limits, accurate quantitation, and high sample throughput.

Methodology

Water samples were acidified to pH ~4 with nitric acid and spiked with known amounts of Cr(III) and Cr(VI) to evaluate recovery. An isocratic IC separation was performed using 0.3 M nitric acid as eluent on a short Dionex IonPac AG7 anion-exchange guard column. A 25 µL injection volume provided baseline resolution of both species within 120 s, and a total run time of 200 s accommodated potential late-eluting peaks at higher concentrations. Calibration curves were generated over 0.1–10 µg/L to assess linearity.

Used Instrumentation

• Ion Chromatography: Thermo Scientific Dionex Aquion IC system with Dionex IonPac AG7 guard column (2 × 50 mm), flow rate 0.4 mL/min, eluent 0.3 mol/L HNO₃, injection volume 25 µL.
• Autosampler: Dionex AS-AP, controlled via ChromControl in Qtegra ISDS software.
• ICP-MS: Thermo Scientific iCAP RQ operated at 1550 W, quartz cyclonic spray chamber (2.7 °C), PFA-LC nebulizer, He collision gas at 4.5 mL/min with 3 V kinetic energy discrimination, dwell time 0.1 s.

Main Results and Discussion

The method achieved complete separation of Cr(III) and Cr(VI) within 120 s. Retention times remained stable over multiple injections (Cr(VI): 36 ± 0.2 s; Cr(III): 101 ± 1.2 s). Detection limits were 4 ng/L for Cr(VI) and 9 ng/L for Cr(III), based on repeated measurements of unspiked tap water. Calibration curves were linear across three orders of magnitude, and spike recoveries in drinking water ranged from 93 ± 1 % for Cr(III) to 113 ± 5 % for Cr(VI), demonstrating accuracy even in complex matrices.

Benefits and Practical Applications

• Rapid analysis with runtimes of ~3 min improves laboratory throughput.
• Low detection limits allow trace-level monitoring of both chromium species.
• Minimal sample preparation and direct coupling reduce contamination risk.
• Guard-column approach balances speed with sufficient resolution for routine water quality testing.

Future Trends and Applications

Advances may include integration of online sample preconcentration for further sensitivity gains, development of portable IC-ICP-MS platforms for field analysis, and expansion of speciation methods to other toxic metal species. Improvements in software automation and streamlined workflows will enhance routine deployment in environmental monitoring and regulatory compliance.

Conclusion

The coupling of a short-column IC method with ICP-MS detection offers a powerful, efficient solution for chromium speciation in drinking water. This approach delivers fast separations, low detection limits, reliable quantitation, and high sample throughput, making it well suited for environmental laboratories and regulatory testing.

Reference

1. Agency for Toxic Substances & Disease Registry. Toxic Substances Portal – Chromium. 2018.
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3. Xing L., Beauchemin D. J. Anal. At. Spectrom. 25 (2010) 1046–1055.
4. Thermo Fisher Scientific. Application Note 43098.