Determination of Trivalent and Hexavalent Chromium in Toy Materials

Importance of the Topic

Chromium exists predominantly in trivalent (Cr(III)) and hexavalent (Cr(VI)) forms. While Cr(III) is a necessary micronutrient, Cr(VI) is a known carcinogen. Regulatory pressures, notably the EU Toy Safety Directive and EN71-3:2019, enforce stringent migration limits for Cr species in toy materials to protect children. Achieving these limits demands highly sensitive and selective analytical approaches capable of discriminating low-level Cr(VI) in the presence of excess Cr(III).

Objectives and Study Overview

This application note describes development and validation of an LC-ICP-MS method for simultaneous speciation and quantification of Cr(III) and Cr(VI) in toy materials. The goals were to meet EN71-3 requirements, attain detection down to single-digit ppt levels after sample preparation, and demonstrate robustness across diverse toy matrices categorized under EN71-3.

Methodology and Instrumentation

Sample Preparation

• Simulated gastric migration according to EN71-3: toy fragments incubated in 0.07 N HCl at 37 °C for 1 h.
• Post-extraction neutralization with ammonia and stabilization by EDTA to prevent species inter-conversion.
• Overall dilution factor of 500× yields target detection levels at ~10 ppt Cr(VI) in solution.

Chromatography and Detection

• Agilent 1260 Bio-inert LC with quaternary pump, bio-inert autosampler, and Bio WAX NP5 anion exchange column (4.6×50 mm, PEEK guard).
• Mobile phase: 75 mM HNO₃ adjusted to pH 7 with ammonia, flow rate 0.8 mL/min, 100 µL injection.
• Agilent 7700x ICP-MS in helium collision mode to remove polyatomic interferences (e.g., ⁴⁰Ar¹²C⁺).
• Cobalt internal standard introduced online for signal drift correction; time-resolved acquisition for m/z 52 (Cr) and 59 (Co ISTD).

Main Results and Discussion

Separation and Sensitivity

• Baseline resolution of Cr(III) and Cr(VI) at 0.95 and 1.67 min.
• Instrument detection limits (3×S/N): 3.1 ppt for Cr(III) and 2.0 ppt for Cr(VI) in solution (equivalent to 1.6 and 1.0 µg/kg in material).
• Method detection limits (3σ of 10 replicates): 8.6 ppt Cr(III) and 2.1 ppt Cr(VI).

Accuracy and Precision

• Spike recoveries between 97 % and 111 % for both species.
• Carryover below 0.01 % of high-concentration load.
• Long-term stability over 50 injections: RSD <5 % for both Cr(III) and Cr(VI).
• Accurate quantification of 0.1 ppb Cr(VI) in presence of 200 ppb Cr(III), with 97 % recovery.

Benefits and Practical Applications

This LC-ICP-MS approach meets EN71-3:2019 requirements for toy safety testing, offering:

• High sensitivity and selectivity for Cr speciation at sub-ppb levels.
• Minimal sample handling and rapid total analysis time (~4 min per injection).
• Robust performance across variable toy matrices (paints, plastics, liquids).
• Automated data integration and ISTD correction for routine QA/QC workflows.

Future Trends and Potential Applications

Advances may include integration of micro-LC for reduced solvent consumption, coupling with high-resolution MS to resolve complex interferences, and expanding speciation to additional regulated elements. Application of similar bio-inert workflows could extend to pharmaceuticals, food contact materials, and environmental monitoring.

Conclusion

An Agilent 1260 Bio-inert LC coupled to a 7700x ICP-MS in He mode provides a reliable, sensitive, and compliant method for Cr(III) and Cr(VI) speciation in toy materials. The protocol fulfills the strict migration limits of EN71-3:2019 and supports regulatory testing under the EU Toy Safety Directive.

References

1. Apostoli P. et al., Elemental speciation in human health risk assessment, WHO, 2006.
2. OEHHA, Public health goal for chromium in drinking water, California EPA, 1999.
3. Directive 2002/95/EC on RoHS, Official Journal EU, L37, 2003.
4. Commission Communication on Directive 2009/48/EC implementation, C282, 2018.