Speciation analysis of Cr (III) and Cr (VI) in drinking waters using anion exchange chromatography coupled to the Thermo Scientific iCAP Q ICP-MS

Significance of the Topic

Speciation of chromium in water is crucial due to the contrasting toxicity and bioavailability of Cr(III) versus Cr(VI). Monitoring individual species enables accurate health risk assessments and regulatory compliance.

Objectives and Study Overview

The main goal was to develop a sensitive, robust, and high-throughput method for trace-level separation and quantification of Cr(III) and Cr(VI) in drinking water using ion chromatography coupled to ICP-MS. Key aspects include:

• Rapid isocratic separation without the need for complexing agents.
• Minimal sample preparation to preserve native species distribution.
• High-sensitivity detection with effective spectral interference suppression.

Methodology and Chromatographic Conditions

Anion-exchange chromatography was performed on a Dionex AG-7 column (2 × 50 mm) using isocratic elution with 0.4 M HNO3 at 400 µL/min. This achieved baseline separation of Cr(III) and Cr(VI) in under 150 s. Calibration curves were established from 0.75 to 15 ng/g, yielding detection limits of 0.20 pg/g for Cr(VI) and 0.38 pg/g for Cr(III). Spike recovery tests demonstrated quantitative recoveries (99–105 %) and excellent precision.

Used Instrumentation

• Dionex ICS-5000 ion chromatography system with a metal-free solvent pathway.
• Dionex AG-7 anion exchange column (2 × 50 mm).
• Thermo Scientific iCAP Qc ICP-MS with flatapole QCell and helium collision mode for interference removal.

Main Results and Discussion

Retention time and peak area reproducibility were maintained below 1.5 % and 0.3 % RSD over 20 consecutive injections. Quantitative spike recoveries confirmed that Cr species remained chemically intact through separation and detection. Application to tap water revealed trace Cr(VI) at 42.5 ± 1 pg/g, validated by the measured 52Cr/53Cr isotope ratio. The combined fast chromatography and interference-free ICP-MS detection enabled reliable sub-ppt speciation analysis.

Practical Applications and Benefits

• Routine compliance monitoring of drinking water for regulatory standards.
• High sample throughput suitable for large-scale environmental surveys.
• Reduced sample handling minimizes contamination risk and preserves species integrity.

Future Trends and Potential Applications

Integration of ultra-fast chromatographic protocols with high-resolution mass spectrometry may further enhance speed and sensitivity. Development of automated, portable IC-ICP-MS platforms could facilitate on-site, real-time water quality monitoring.

Conclusion

The described IC–ICP-MS method provides a rapid, robust, and highly sensitive approach for chromium speciation in water. Its minimal sample preparation, high throughput, and reliable quantification make it well suited for regulatory and research laboratory applications.

References

• Séby F., Charles S., Gagean M., Garraud H., Donard O.F.X., J. Anal. At. Spectrom. 18 (2003): 1386–1390.
• Xing L., Beauchemin D., J. Anal. At. Spectrom. 25 (2010): 1046–1055.
• Dionex product documentation: IonPac AG-7 column specifications.