Determination of Hexavalent Chromium in Dyes

Importance of the Topic

Hexavalent chromium (Cr(VI)) is the most toxic oxidation state of chromium and is strictly regulated in drinking water and consumer products. Leather dyes often contain trivalent chromium, which can oxidize to Cr(VI) and migrate to the skin via sweat. Reliable monitoring of Cr(VI) in dyes is critical for consumer safety, regulatory compliance, and industrial quality control.

Objectives and Study Overview

This study demonstrates a sensitive and accurate ion chromatography (IC) method with postcolumn reaction for the determination of Cr(VI) in two commercial dyes, Fast Red and Metal Complex Black. The aim is to evaluate method performance in terms of detection capability, accuracy, and applicability to real samples.

Instrumentation Used

• Thermo Scientific Dionex ICS-3000 system with DP dual pump, visible absorbance detector (VWD), and AS autosampler
• Dionex IonPac AS7 Analytical column (4 × 250 mm) with Dionex IonPac NG1 guard column (4 × 50 mm)

Methodology

Chromatographic and detection conditions:

• 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 and 1 N sulfuric acid; reaction coil: 1,500 µL; reagent flow: 0.5 mL/min
• Detection: visible absorbance at 530 nm
• Sample preparation: dyes diluted 1:100 in deionized water, then cleaned on OnGuard II P cartridges

Main Results and Discussion

Analysis of 1:100 dilutions revealed:

• Fast Red: no detectable Cr(VI)
• Metal Complex Black: 56.1 µg/L Cr(VI)
• Spike recovery (30 µg/L added): 99.3% for Fast Red, 101% for Metal Complex Black

The method exhibits low detection limits, good linearity, and robustness under typical backpressures of 1,200–1,300 psi. The postcolumn reaction generates a colored complex for selective visible detection, ensuring high specificity.

Benefits and Practical Applications

The IC method is fast, simple, and highly sensitive, allowing accurate quantification of trace Cr(VI) in dye formulations. It is well suited for routine quality control in textile, leather, and consumer product industries, as well as for regulatory laboratories assessing Cr(VI) migration risks.

Future Trends and Potential Applications

Advances may include integration of automated sample preparation, miniaturized IC systems for field or at‐line testing, and coupling with mass spectrometry for multi-element speciation. Expansion to a wider range of consumer goods and real-time monitoring platforms could further enhance safety assurance.

Conclusion

The presented ion chromatography method with postcolumn diphenylcarbazide reaction offers a reliable, accurate, and sensitive approach for Cr(VI) determination in dye samples. Its performance meets regulatory requirements and supports industrial QA/QC workflows.

References

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, Sunnyvale, CA.