Determination of Trivalent and Hexavalent Chromium in Toy Materials

Significance of the Topic

Chromium exists mainly as CrIII and CrVI. CrIII is an essential trace element while CrVI is classified as a carcinogen. European Toy Safety Standard EN71-3 regulates migration of toxic elements from toy materials to protect children from exposure through chewing or ingestion. CrVI limits are especially stringent, requiring analytical methods capable of ppt level detection.

Objectives and Study Overview

The aim was to develop and validate a method for separation and quantification of CrIII and CrVI in toy materials following EN71-3 revision 2019. The method needed to achieve low detection limits after a 500x dilution sample preparation simulating gastric digestion.

Methodology and Instrumentation

• Sample Preparation: Toy fragments treated with dilute HCl at 37°C for one hour. Extracts neutralized with ammonia and stabilized with EDTA to prevent interconversion.
• Chromatography: Agilent 1260 Bio-inert LC with anion exchange WAX NP5 column. Mobile phase was 75 mM HNO3 adjusted to pH 7 with ammonia. Flow rate 0.8 mL/min, injection volume 100 µL.
• ICP-MS Detection: Agilent 7700x ICP-MS in helium collision mode to remove polyatomic interferences. Cobalt used as on-line internal standard. Time resolved analysis with dwell times of 1.0 s for m/z 52 and 0.1 s for m/z 59.

Key Results and Discussion

Retention times for CrIII and CrVI were 0.95 and 1.67 minutes, respectively. Method detection limits in solution were 3.1 ppt for CrIII and 2.0 ppt for CrVI. Method detection limits in material correspond to 1.6 µg/kg and 1.0 µg/kg. Spike recoveries ranged from 97 to 112 for CrIII and 96 to 111 for CrVI. Carryover was below 0.01. The method reliably quantified 0.1 ppb CrVI in the presence of 200 ppb CrIII with 97 percent recovery and RSD below 5 over 50 samples, demonstrating minimal peak tailing and excellent stability.

Benefits and Practical Applications

• Meets EN71-3:2019 requirements for Cr speciation in toy safety testing.
• Single digit ppt detection with robust peak separation ensures accurate quantitation even in high CrIII backgrounds.
• Bio-inert LC hardware minimizes metal contamination and species conversion.
• Suitable for routine quality control in laboratories and regulatory compliance testing.

Future Trends and Potential Applications

• Extending the approach to other regulated elements and complex matrices such as textiles or plastics.
• Integration with automated sample preparation workflows for higher throughput.
• Advancements in microflow LC and novel collision gases may further improve sensitivity and separation.

Conclusion

The developed LC-ICP-MS method provides sensitive, accurate, and reproducible speciation of CrIII and CrVI in toy materials. It fully supports EN71-3:2019 compliance by delivering required detection limits, high recovery, and minimal carryover in routine analysis.

Reference

1. Apostoli P Bartels M Chen T et al Elemental speciation in human health risk assessment World Health Organization 2006
2. OEHHA Public health goal for chromium in drinking water California Environmental Protection Agency 1999
3. Directive 2002/95/EC of the European Parliament and of the Council Restriction of Hazardous Substances 2003
4. Commission communication on implementation of Directive 2009/48/EC on toy safety Official Journal of the European Union 2018