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

Significance of the Topic

The speciation of chromium in drinking water is critical because hexavalent chromium (Cr(VI)) is toxic and carcinogenic, whereas trivalent chromium (Cr(III)) is an essential nutrient. Accurate, rapid, and sensitive methods for distinguishing these two forms support regulatory compliance, protect public health, and guide treatment processes.

Objectives and Study Overview

This study evaluates an ion chromatography–inductively coupled plasma mass spectrometry (IC-ICP-MS) method for the separation and low-level detection of Cr(III) and Cr(VI) in drinking water. The method is based on EPA Method 218.7 but replaces UV detection with ICP-MS to improve sensitivity and streamline routine speciation analysis.

Methodology and Instrumentation

Sample preservation was achieved by adding EDTA (2 mM) and an ammonium sulfate/ammonium hydroxide buffer to prevent species interconversions. A Metrohm 940 IC fitted with a Metrosep ASUPP4 250/4.0 column and a 10 mM ammonium nitrate mobile phase (2 mM EDTA, pH 10) delivered baseline separation of Cr(III) and Cr(VI) within four minutes.
The IC system was coupled to an Agilent 7800 ICP-MS operated with an ORS4 collision/reaction cell in helium mode to remove ArC polyatomic interferences at m/z 52. Time-resolved analysis with 0.5 s integration over a 6 min run provided quantitative data.

Main Results and Discussion

Calibration curves for both Cr species were linear (r² = 1.0000) over 0.01–10 µg/L. Method Detection Limits (MDLs) were 0.006 µg/L for Cr(III) and 0.003 µg/L for Cr(VI), based on replicate blank spikes. Proposed Minimum Reporting Limits (MRLs) of 0.025 µg/L (Cr(III)) and 0.020 µg/L (Cr(VI)) were confirmed by recovery tests meeting EPA 218.7 criteria (50–150 % recovery at 99.5% confidence).
Spike recoveries in two tap water samples demonstrated that the preservative buffer prevented species interconversion, yielding recoveries of 89–104% for Cr(III) and Cr(VI). Retention time stability was excellent (RSD <1% for Cr(III), <0.1% for Cr(VI)) over multiple days.

Benefits and Practical Applications

• Fast sample-to-sample time (<10 min including rinsing).
• High sensitivity and low MDLs support compliance with WHO, EPA, and state drinking water standards.
• Metal-free IC flow path reduces contamination risk and maintenance costs.
• Simple sample preparation and robust operation enable use by nonexpert analysts.
• Simultaneous quantification of Cr(III) and Cr(VI) in a single run improves laboratory efficiency.

Future Trends and Potential Applications

Advances may include on-line sample filtration and derivatization, miniaturized IC-ICP-MS systems for field or mobile laboratories, and expansion to other redox-sensitive metals. Integration with automated data processing and real-time monitoring platforms could further enhance regulatory surveillance and water quality management.

Conclusion

The combined Metrohm 940 IC and Agilent 7800 ICP-MS method delivers fast, accurate, and sensitive speciation of Cr(III) and Cr(VI) in drinking water. It meets stringent regulatory limits, offers low detection and reporting limits, and is well suited for routine monitoring in environmental and industrial laboratories.

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