WCPS: Chromium Speciation in Drinking Water using LC(IC)--ICPICP--MSMS

Importance of the Topic

Chromium occurs in two major oxidation states in water: the toxic hexavalent form Cr(VI) and the essential trivalent form Cr(III). Regulatory agencies worldwide are tightening limits on Cr(VI) in drinking water due to its carcinogenicity. Accurate speciation at ultra-trace levels is critical for risk assessment and ensuring public safety.

Objectives and Study Overview

This work aimed to develop a fast, isocratic HPLC–ICP-MS method to separate and quantify Cr(III) and Cr(VI) in highly mineralized drinking waters in under four minutes. The study demonstrated method performance in spiked and unspiked natural waters, evaluated detection limits, precision, and long-term stability, and compared conventional versus bio-inert liquid chromatography systems.

Methodology and Instrumentation

The separation was performed on an anion-exchange column with a mobile phase of 5 mM EDTA, 5 mM NaHPO4, and 15 mM Na2SO4 at pH 7.0, delivered at 1.2 mL/min. Injection volumes ranged from 5 to 1500 µL to optimize sensitivity. Cr species were detected using ICP-MS in helium collision mode to minimize polyatomic interferences. Method validation covered linearity, detection limits, reproducibility, and spike recovery in complex matrices.

Used Instrumentation

• Agilent 1200 HPLC with binary pump, autosampler, vacuum degasser and bio-compatibility kit
• Anion-exchange column (4.6 mm × 30 mm) with polyhydroxymethacrylate resin
• Agilent 7700x ICP-MS, RF power 1550 W, helium collision gas, monitoring isotopes 52Cr and 53Cr
• Mobile phase: 5 mM EDTA, 5 mM NaHPO4, 15 mM Na2SO4, adjusted to pH 7.0 with NaOH
• Flow rate 1.2 mL/min, injection volumes up to 1500 µL

Main Findings and Discussion

The method achieved baseline separation of Cr(III) and Cr(VI) within four minutes. At a 100 µL injection, detection limits were <0.2 µg/L for both species, improving to 8 ng/L for Cr(VI) at 1500 µL. Long-term stability over eight hours showed relative standard deviations below 5%. Spike recoveries in high-matrix waters (up to 450 ppm Ca and 1121 ppm sulfate) ranged from 91% to 99%. Use of a bio-inert pump reduced background signals, further enhancing sensitivity.

Benefits and Practical Applications

• Rapid throughput for routine monitoring of drinking water and environmental samples
• Ultra-trace quantification of toxic Cr(VI) alongside essential Cr(III)
• Robust performance in high-mineral content matrices without suppression or retention shifts
• Flexibility to switch between conventional and bio-inert systems for optimized detection limits

Future Trends and Opportunities

Advances may include further purification of mobile phase reagents to lower background, miniaturized or field-deployable LC-ICP-MS systems for on-site monitoring, and integration with high-resolution mass spectrometry for simultaneous multi-element speciation. Emerging regulatory demands will drive automation and real-time data analysis for rapid decision-making.

Conclusion

The proposed isocratic LC–ICP-MS method delivers fast, sensitive, and reliable separation and quantification of Cr(III) and Cr(VI) in drinking water. Its high reproducibility, low detection limits, and robustness in high-matrix samples make it a valuable tool for laboratories tasked with ensuring compliance with increasingly stringent chromium regulations.