Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography

Importance of the Topic

Hexavalent chromium [Cr(VI)] is a highly toxic form of chromium that poses significant health risks, including respiratory, hepatic, and renal damage. In contrast, trivalent chromium [Cr(III)] is an essential nutrient for mammalian metabolism. Accurate and reliable quantification of Cr(VI) at low concentrations is critical for regulatory compliance, environmental monitoring, and industrial wastewater management.

Objectives and Study Overview

This application note describes a sensitive ion chromatography (IC) method for determining dissolved Cr(VI) as chromate (CrO42–) down to 1 μg/L in various water matrices, including drinking water, groundwater, and industrial effluents. The method aligns with established protocols from the U.S. EPA and ASTM, and has been validated over a concentration range of 1–1000 μg/L.

Methodology and Instrumentation

Sample Preparation and Eluent Composition:

• Eluent: 250 mM ammonium sulfate and 100 mM ammonium hydroxide in water.
• Sample volume: 50 μL per injection.

Chromatographic Separation:

• Column: Anion‐exchange Thermo Scientific™ Dionex™ IonPac™ AS7 analytical column with a Dionex IonPac NG1 guard column.
• Flow rate: 1.5 mL/min.
• Operating pressure: 900–1100 psi.

Postcolumn Derivatization and Detection:

• Reagent: 2.0 mM 1,5‐diphenylcarbazide in 10% methanol and 1.0 N sulfuric acid.
• Reagent flow rate: 0.5 mL/min.
• Detection: Visible absorbance at 530 nm to monitor the colored complex formed with Cr(VI).

Instrumentation

Any Dionex ion chromatography system* equipped with:

• UV/Visible absorbance detector (VDM‐2 or equivalent).
• Postcolumn reagent delivery module.

* Equivalent performance achievable on Thermo Scientific Dionex ICS‐2100 or ICS‐5000+ systems.

Main Results and Discussion

The IC method demonstrated a method detection limit near 1 μg/L and a linear response up to 1000 μg/L. Figure 1 (area response plot) and Figure 2 (chromatogram) confirm baseline separation of chromate, with stable peak shapes and reproducible retention times. The colorimetric detection step yields a strong signal-to-noise ratio, enabling trace quantification in complex matrices.

This approach is specific for Cr(VI) and does not measure total chromium. Total chromium determination requires acid digestion to convert all species to Cr(III) before analysis by alternative methods.

Benefits and Practical Applications

• High sensitivity and selectivity for Cr(VI) at regulatory levels.
• Rapid analysis with minimal sample preparation.
• Compatibility with drinking water, groundwater, wastewater, and particulate extracts.
• Compliance with U.S. EPA and ASTM recommended protocols.

Future Trends and Potential Applications

• Integration with mass spectrometric detectors for enhanced selectivity and speciation studies.
• Automation and inline sample pretreatment for high-throughput monitoring.
• Miniaturized and portable IC systems for field measurements.
• Extended application to solid‐phase extracts, air particulate samples, and industrial process streams.

Conclusion

The described ion chromatography method with postcolumn colorimetric detection offers a robust, accurate, and sensitive solution for routine determination of dissolved hexavalent chromium in diverse environmental waters. Its alignment with regulatory standards and proven performance make it a valuable tool for laboratories engaged in water quality assessment and industrial effluent monitoring.

Reference

1. Arar EJ, Long SE, Pfaff JD. Method 218.6 Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater, and Industrial Wastewater Effluents by Ion Chromatography. U.S. EPA; 1991.
2. Arar EJ, Pfaff JD. J Chromatogr Sci. 1991;546:335–340.
3. ASTM Committee D-19. Proposed Method: Dissolved Hexavalent Chromium in Water by Ion Chromatography. ASTM; 1991.
4. ASTM Committee D-22. Proposed Method: Collection and Analysis of Hexavalent Chromium in the Atmosphere. ASTM; 1991.
5. Edgell K, Longbottom J, Joyce R. Collaborative Study: Dissolved Hexavalent Chromium in Water by Ion Chromatography. U.S. EPA; 1991.
6. Pappa R, Castillo N. Determination of Ambient Levels of Hexavalent Chromium by Ion Chromatography. California Air Resources Board; 1989.
7. U.S. EPA. Methods Manual for Compliance With BIF Regulations: Determination of Hexavalent Chromium Emissions. 1990.