Determination of Hexavalent Chromium in Dyes

Importance of the Topic

Divalent and hexavalent chromium species differ drastically in toxicity, with Cr(VI) being highly toxic and regulated in water and consumer products. In textile and leather industries, Cr(III)-based dyes may oxidize to Cr(VI) under use or storage conditions, posing health and regulatory risks. Sensitive detection of residual Cr(VI) in dyes ensures consumer safety and compliance with environmental and product standards.

Study Objectives and Overview

This application brief describes an ion chromatography (IC) technique combined with postcolumn reaction for selective, accurate quantification of trace Cr(VI) in dye samples. Two commercial dyes—Fast Red and Metal Complex Black—were analyzed at 1:100 dilution. The method’s aim was to determine Cr(VI) concentration with high sensitivity and evaluate recovery through spiking experiments.

Methodology and Instrumentation

The analytical setup comprised a Thermo Scientific™ Dionex™ ICS-3000 system with a dual-pump, VWD absorbance detector, and AS autosampler. Chromatographic separation used a Dionex IonPac™ AS7 Analytical column (4 × 250 mm) with a NG1 guard (4 × 50 mm). Key parameters:

• Eluent: 250 mM ammonium sulfate, 100 mM ammonium hydroxide
• Column temperature: 30 °C
• Flow rate: 1.0 mL/min, injection volume: 10 µL
• Postcolumn reagent: 2 mM diphenylcarbazide in 10% methanol, 1 N sulfuric acid
• Reaction coil volume: 1500 µL, PCR flow rate: 0.5 mL/min
• Detection: visible absorbance at 530 nm
• OnGuard™ II P cartridge for sample cleanup

Key Results and Discussion

Chromatograms revealed no detectable Cr(VI) in Fast Red dye at 1:100 dilution, while Metal Complex Black contained 56.1 µg/L Cr(VI). Spiking both samples with 30 µg/L Cr(VI) gave recoveries of 99.3% for Fast Red and 101% for Metal Complex Black. The baseline resolution of Cr(VI) peak, low backpressure (1200–1300 psi), and negligible interference demonstrate method robustness. The data confirm that the method can detect trace Cr(VI) in complex dye matrices with high accuracy and precision.

Benefits and Practical Applications

This IC method offers multiple advantages:

• High sensitivity and selectivity for Cr(VI)
• Minimal sample preparation and rapid analysis turnaround
• Strong accuracy demonstrated by spike recoveries near 100%
• Applicability to regulatory compliance testing of dyes and leather products

Future Trends and Opportunities

Emerging areas include coupling IC with mass spectrometry for multi-element speciation, miniaturized portable IC systems for field monitoring, and integration with automated sample handling to further increase throughput. Advances in reagent chemistries may improve detection limits and matrix tolerance.

Conclusion

The presented IC method with postcolumn diphenylcarbazide reaction provides an effective tool for quantitative analysis of Cr(VI) in dye samples. Its accuracy, reproducibility, and speed make it suitable for routine quality control and regulatory testing in textile and leather industries.

Reference

1. Peterson J.; Murphy B.; Perati P.; Richter B. LCGC The Applications Notebook, 2007, June, 28.
2. Dionex Application Update 144, Determination of Hexavalent Chromium in Drinking Water Using Ion Chromatography, LPN 1495, 2003.