Simultaneous Determination of Trivalent Chromium and Hexavalent Chromium Using Accelerated Solvent Extraction and Ion Chromatography

Importance of the Topic

The simultaneous quantification of trivalent and hexavalent chromium is critical due to their distinct toxicity profiles and regulatory limits. Cr(III) is an essential nutrient at low concentrations but can be cytotoxic at higher doses, while Cr(VI) is highly oxidizing and carcinogenic. Accurate differentiation and measurement of both species in diverse matrices such as toys, soil, industrial materials and consumer products is essential for health protection and compliance with regulations like the EU Toy Safety Directive.

Objectives and Study Overview

This study aimed to develop a rapid, sensitive and robust method for concurrent extraction and analysis of Cr(III) and Cr(VI). The approach integrates accelerated solvent extraction (ASE) with tailored precolumn and postcolumn derivatization followed by ion chromatography (IC). Various real-world samples including plastic, rubber, textiles, leather, soil and waste materials were evaluated to demonstrate method applicability.

Methodology and Instrumentation

The extraction solvent comprised pyridinedicarboxylic acid (PDCA), potassium iodide, ammonium acetate and lithium hydroxide, serving both extraction and precolumn derivatization of Cr(III). ASE was performed at 100 °C for two 5 min static cycles using Dionium extraction cells to avoid metal contamination. Extracts were volume-adjusted, filtered and introduced into a reagent-free IC system. IonPac CS5A guard and analytical columns were used with a 1 mL/min eluent flow. Postcolumn addition of 2 mmol/L diphenylcarbazide reagent at 0.5 mL/min selectively derivatized Cr(VI) detected at 530 nm, while Cr(III) was monitored at 335 nm without postcolumn reagent. Reaction coil volume (375 µL) and temperature (30 °C) were optimized for maximum sensitivity.

Main Results and Discussion

The method achieved limits of detection of 0.5 ng/mL for Cr(VI) and 5 ng/mL for Cr(III) with linear ranges up to 100 ng/mL and 1000 ng/mL, respectively (r²>0.999). Conversion tests confirmed negligible interconversion during extraction, with recoveries exceeding 97% for both species. Matrix spike recoveries ranged from 90.5% to 101.2% (RSD<4.5%). Blank tests showed stainless steel cells leached Cr(III), whereas Dionium cells remained free of contamination. Analysis of real samples revealed Cr(III) in leather, textiles and other materials, with Cr(VI) levels generally below detection.

Benefits and Practical Applications of the Method

The combined ASE–IC approach offers high throughput, minimal sample preparation and excellent sensitivity for chromium speciation. Use of inert extraction cells eliminates contamination risk. This method supports quality control in consumer products, environmental monitoring, industrial process control and regulatory compliance testing.

Future Trends and Potential Applications

Emerging developments may include miniaturized and automated ASE systems, coupling IC with mass spectrometry for enhanced selectivity, adoption of greener solvents and integration into online monitoring platforms. Expansion to additional metal species and multiplexed analyses is anticipated.

Conclusion

This work demonstrates that accelerated solvent extraction combined with optimized IC derivatization enables accurate, sensitive and efficient simultaneous analysis of Cr(III) and Cr(VI). The method is robust across diverse matrices and meets stringent regulatory requirements.

References

1. Li J., Wang Y., Chen H., Liang L. Simultaneous Extraction and Determination of Chromium (III) and Chromium (VI) in Milk. Food Science. 2010;31(10):250–253.
2. Dionex (Thermo Scientific). Technical Note 24: Determination of Chromium by Ion Chromatography. Sunnyvale, CA; accessed Dec 13, 2013.