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

Significance of the Topic

Hexavalent chromium (Cr(VI)) is a recognized environmental contaminant with known toxicity to the respiratory, hepatic, and renal systems. Monitoring Cr(VI) at low microgram-per-liter levels in drinking water, groundwater, and industrial effluents is critical for public health and regulatory compliance. Ion chromatography coupled with postcolumn colorimetric detection provides selective and sensitive quantitation of the chromate anion in complex matrices.

Objectives and Study Overview

This application note describes a validated ion chromatographic method for determining dissolved Cr(VI) as CrO42– in environmental waters. Key goals include achieving a detection limit near 1 µg/L, demonstrating method linearity from 1 to 1 000 µg/L, and verifying applicability across drinking water, groundwater, wastewater, and solid-waste extracts.

Methodology and Instrumentation

Samples are injected (50 µL) onto a Thermo Scientific Dionex IonPac AS7 analytical column with a NG1 guard. Separation is achieved using an eluent of 250 mM ammonium sulfate and 100 mM ammonium hydroxide at 1.5 mL/min. Postcolumn, 2 mM diphenylcarbazide in 10% methanol and 1 N sulfuric acid is delivered at 0.5 mL/min. The resulting chromium–reagent complex absorbs at 530 nm, detected by a UV/Visible absorbance detector (VDM-2 or equivalent). Reagents and standards are prepared as follows:

• Eluent: Dissolve 33 g ammonium sulfate and add 6.5 mL ammonium hydroxide to 500 mL water, dilute to 1 L.
• Postcolumn reagent: Dissolve 0.50 g diphenylcarbazide in 100 mL methanol, add 500 mL water with 28 mL sulfuric acid, dilute to 1 L.
• Primary standard: 0.283 g dried potassium dichromate in 100 mL water yields 1 000 mg/L Cr(VI).

Main Results and Discussion

Method detection limits around 1 µg/L were achieved in both drinking water and wastewater matrices. Calibration is linear from 1 to 1 000 µg/L. Chromatograms show clear separation of Cr(VI) with reproducible retention times under the specified conditions. The postcolumn colorimetric approach ensures selectivity by reacting exclusively with Cr(VI), avoiding interference from Cr(III) or other anions. Note that total chromium determination requires prior acid digestion converting all forms to Cr(III) and is outside this method’s scope.

Benefits and Practical Applications

This ion chromatography method offers:

• High sensitivity meeting regulatory limits for potable and industrial waters.
• Robust selectivity via postcolumn colorimetry.
• Wide dynamic range for varied sample concentrations.
• Compatibility with standard environmental monitoring and U.S. EPA reference methods.

Future Trends and Potential Applications

Advances in column chemistries and detector technologies may further lower detection limits and reduce analysis times. Potential extensions include on-line sample pretreatment for automated monitoring, coupling with mass spectrometry for speciation studies, and miniaturized systems for field deployment.

Conclusion

The described ion chromatographic procedure provides a validated, reliable, and sensitive approach for determining dissolved hexavalent chromium in diverse environmental waters. Its compliance with standard methods and robust performance make it well suited for routine monitoring and regulatory applications.

Reference

1. Arar E.J.; Long S.E.; Pfaff J.D., Method 218.6, U.S. EPA, 1991.
2. Arar E.J.; Pfaff J.D., J. Chromatogr. Sci. 1991, 29, 335–340.
3. ASTM D19. Proposed Method “Dissolved Hexavalent Chromium in Water by Ion Chromatography,” 1991.
4. ASTM D22. Proposed Method “Collection and Analysis of Hexavalent Chromium in the Atmosphere,” 1991.
5. Edgell K.; Longbottom J.; Joyce R., Collaborative Study Report, U.S. EPA, 1991.
6. Pappa R.; Castillo N., CARB Ambient Levels Study, 1989.
7. U.S. EPA Methods Manual for BIF Regulations, 1990.