Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography (IC)–ICP-MS

Significance of the Topic

Chromium exists in two main species: Cr(III), essential in trace amounts, and Cr(VI), toxic and carcinogenic. Monitoring hexavalent chromium in drinking water is critical due to its health risks and evolving regulatory limits worldwide. A cost-effective, reliable analytical method for distinguishing and quantifying each species at trace levels supports public safety and compliance.

Objectives and Study Overview

This study aimed to develop and validate a rapid ion chromatography (IC)–ICP-MS technique for separate detection of Cr(III) and Cr(VI) in drinking water. Building on EPA Method 218.7, the work assessed method and instrument parameters, determined minimum reporting limits (MRLs) and method detection limits (MDLs), and demonstrated robustness through spike recovery tests in tap water.

Methodology

• Sample Preservation: Addition of EDTA (2 mM) and ammonium sulfate/ammonium hydroxide buffer to stabilize Cr species and prevent interconversion.
• Chromatographic Conditions: Metrosep ASUPP4 column with 10 mM ammonium nitrate and 2 mM EDTA at pH 10; flow rate 1.0 mL/min; 250 µL injection; total run time ≤ 6 min.
• Calibration: Eight-point curves from 0.01 to 10 µg/L for both species; linearity R² = 1.0000.
• MRL and MDL Determination: MRLs proposed at 0.025 µg/L for Cr(III) and 0.020 µg/L for Cr(VI) were confirmed via replicate spiking and statistical RPIR criteria; MDLs calculated as 0.006 µg/L and 0.003 µg/L.

Instrumentation

• IC System: Metrohm 940 Professional IC with metal-free sample path and Metrosep ASUPP4 250/4.0 column.
• ICP-MS Detector: Agilent 7800 ICP-MS using He collision mode (KED) in the ORS4 cell to eliminate ArC interferences at m/z 52.
• Data Acquisition: Time Resolved Analysis mode, 0.5 s integration, 6 min per run.

Main Results and Discussion

• Separation Efficiency: Baseline resolution of Cr(III) and Cr(VI) within 4 min, enabling high throughput.
• Signal Stability: Retention time RSD <1% for Cr(III) and <0.1% for Cr(VI) over multiple days.
• Spike Recoveries: Tap water samples showed 94–104% recovery of Cr(VI) and 89–128% of Cr(III) with preservative, confirming method accuracy and effective species stabilization.
• Compliance: MRLs and MDLs meet stringent EPA and California public health goals for chromium in drinking water.

Benefits and Practical Applications

• Fast, sensitive, and accurate quantification of chromium species at sub-µg/L levels.
• Reduced operational cost with a metal-free IC system and minimal sample preparation.
• Suitable for routine environmental monitoring, QA/QC labs, and regulatory compliance testing.

Future Trends and Opportunities

Analytical developments may include shorter columns or gradient methods for faster separations, automation of sample handling, and expansion to speciation of other redox-sensitive metals. Integration with advanced data analytics and remote monitoring could further enhance field-deployable chromium speciation.

Conclusion

The validated IC–ICP-MS method provides a robust, high-throughput approach for accurate speciation and quantification of Cr(III) and Cr(VI) in drinking water. It fulfills regulatory requirements, supports environmental safety, and offers practical efficiency for routine laboratory operations.

References

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• 2. Ezebuiro P, Gandhi J, Zhang C, et al. Optimal Sample Preservation and Analysis of Cr(VI) in Drinking Water by Ion Chromatography and UV/Vis Spectroscopy. JASMI. 2012;2(2):74–80.
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• 4. Buerge IJ, Hug SJ. Kinetics and pH Dependence of Cr(VI) Reduction by Fe(II). Environ Sci Technol. 1997;31:1426–1432.
• 5. US EPA. Chromium in Drinking Water. 2021.
• 6. WHO. Chromium in Drinking Water: Background Document. 2003.
• 7. Directive (EU) 2020/2184 on the quality of water intended for human consumption. 2020.
• 8. California OEHHA. Public Health Goal for Cr(VI) in Drinking Water. 2011.
• 9. EPA Method 218.7. Determination of Hexavalent Chromium by IC with UV-Vis. 2011.
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