Speciation Analysis of Chromium by LC-ICP-MS Based on ISO 24384

Significance of the Topic

Chromium exists mainly as Cr(III) and highly toxic Cr(VI), making their speciation critical in environmental and regulatory contexts. Liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP-MS) allows simultaneous and selective determination of both forms, reducing matrix interferences and complying with ISO 24384.

Study Objectives and Overview

This application demonstrates the simultaneous quantification of Cr(III) and Cr(VI) in various water matrices using an LC-ICP-MS method based on ISO 24384. A Shimadzu Prominence Inert LC system was interfaced with an ICPMS-2050 to evaluate method performance in mineral water, tap water, river water, and wastewater samples.

Methodology and Instrumentation Used

• Sample pretreatment: filtration (0.45 µm), pH adjustment to ~6.9, addition of EDTA chelating agent, heating at 70 °C for 60 minutes, and final filtration (0.2 µm).
• LC conditions: anion exchange column (Shodex SI-35-4D, 150 mm × 4.0 mm, 3.5 µm) with a guard column (Shodex SI-95(G)), mobile phase 100 mmol/L HNO₃ (pH 7.0), flow rate 0.45 mL/min, column temperature 25 °C, injection volume 200 µL.
• ICP-MS conditions: ICPMS-2050 with Nebulizer DC04, mini torch, cyclone chamber, nickel sampling and skimmer cones; RF power 1.2 kW; plasma, auxiliary, carrier, and dilution gas flows set to 9.0, 1.1, 0.45, and 0.40 L/min respectively; helium cell gas at 3.5 mL/min; cell voltage –15 V; energy filter 7 V; monitoring Cr at m/z 52.

Key Results and Discussion

Chromatographic separation achieved baseline resolution (R = 4.4) between Cr(III)-EDTA and Cr(VI). Calibration curves for both species were linear over 0.05–20 µg/L (R² > 0.9999). Detection limits (3σ) in measurement solution were approximately 0.015 µg/L for Cr(III) and 0.006 µg/L for Cr(VI). Spike recovery tests in diverse water samples ranged from 97% to 109%, within ISO acceptance (80–120%), and total chromium speciation matched total Cr measurements within 30%, indicating minimal interferences.

Benefits and Practical Applications

• Simultaneous speciation of Cr(III) and Cr(VI) with high selectivity.
• Reduced sample preparation complexity compared to conventional methods.
• Compliance with ISO 24384 for water quality analysis.
• Easy system integration by direct LC outlet connection to ICP-MS nebulizer.

Future Trends and Opportunities

The method can be extended to other trace metal speciation, incorporate advanced collision/reaction cell technologies, and be adapted for automated or portable platforms. Integration with hyphenated techniques may further enhance selectivity and throughput.

Conclusion

The described LC-ICP-MS approach using EDTA chelation and simple pretreatment provides a robust, sensitive, and ISO-compliant solution for simultaneous chromium speciation in environmental waters, with strong linearity, low detection limits, and excellent recovery.

References

• ISO 24384:2024 Water quality — Determination of chromium(VI) and chromium(III) in water — Method using liquid chromatography with inductively coupled plasma mass spectrometry (LC-ICP-MS) after chelating pretreatment. Edition 1, 2024.