Determination of chromium species using ion chromatography coupled to inductively coupled plasma mass spectrometry

Importance of the Topic

Chromium exists in multiple oxidation states with contrasting biological and environmental impacts. Trivalent chromium (Cr(III)) is an essential micronutrient, whereas hexavalent chromium (Cr(VI)) is highly toxic and carcinogenic. Reliable speciation of these forms in water is critical for accurate risk assessment and regulatory compliance.

Goals and Study Overview

This study aimed to develop a fast, robust method to separate and quantify Cr(III) and Cr(VI) in drinking water. Combining ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS) enables sensitive detection and precise speciation within a short analysis time.

Methodology and Instrumentation

Samples of tap water were acidified to pH ~4 and spiked for calibration. An isocratic IC separation used 0.3 M nitric acid on a short anion‐exchange guard column, achieving baseline separation in under 2 minutes. The column outlet was directly coupled to the ICP-MS using a PFA-LC nebulizer and zero-dead-volume connector. Kinetic energy discrimination with helium collision gas removed polyatomic interferences on the 52Cr isotope.

Used Instrumentation

• Ion Chromatography: Thermo Scientific Dionex Aquion IC with IonPac AG7 guard column and AS-AP autosampler
• Eluent: 0.3 mol/L HNO₃, flow rate 0.4 mL/min, injection volume 25 µL
• ICP-MS: Thermo Scientific iCAP RQ with quartz cyclonic spray chamber (2.7 °C), PFA-LC nebulizer, Ni sampler/skimmer cones, He collision gas, KED mode
• Software: Qtegra ISDS with ChromControl and tQuant modules

Key Findings and Discussion

• Complete separation of Cr(VI) at 36 ± 0.2 s and Cr(III) at 101 ± 1.2 s, with elution within 120 s and extended runtime to 200 s for higher loads.
• Linearity over 0.1–10 µg/L, sensitivities of 114 kcps/(µg/L) for Cr(VI) and 123 kcps/(µg/L) for Cr(III).
• Detection limits of 4 ng/L (Cr(VI)) and 9 ng/L (Cr(III)) based on repeated blank injections.
• Stable retention times over 10 injections; spike recoveries of 93 ± 1 % for Cr(III) and 113 ± 5 % for Cr(VI) in real water samples.

Benefits and Practical Applications

The short run time (≈3 min), minimal column contamination, and high sensitivity make this IC-ICP-MS approach ideal for high-throughput drinking water analysis in environmental monitoring, water treatment facilities, and regulatory labs. Fast speciation supports timely decision-making on water safety.

Future Trends and Potential Applications

• Extension to other redox‐active metal species (e.g., arsenic, selenium) using tailored eluent compositions.
• Automation and coupling with robotic sample preparation for large‐scale monitoring networks.
• Integration with online preconcentration techniques to push detection limits into sub-ng/L levels.
• Development of field-portable IC-ICP-MS systems for on-site speciation in remote locations.

Conclusion

The described method achieves rapid, accurate chromium speciation with excellent sensitivity and robustness. The streamlined workflow, combining a short IC guard column and direct IC-MS interfacing, delivers high throughput without sacrificing analytical performance, making it a valuable tool for environmental and industrial water quality control.

References

1. Agency for Toxic Substances and Disease Registry. Toxic Substances Portal – Chromium. 2018.
2. Séby F., Charles S., Gagean M., Garraud H., Donard O.F.X. J. Anal. At. Spectrom. 18 (2003) 1386–1390.
3. Xing L., Beauchemin D. J. Anal. At. Spectrom. 25 (2010) 1046–1055.
4. Thermo Fisher Scientific. Application Note 43098.