Accurate Quantification of Cadmium, Chromium, Mercury and Lead in Plastics for RoHS Compliance using the Agilent 7500ce ICP-MS

Importance of the Topic

The Restriction of Hazardous Substances (RoHS) Directive drives the need for precise, traceable quantification of cadmium, chromium, mercury and lead in plastic components of electronic and consumer products. Reliable analytical methods enable compliance testing laboratories to support international trade by ensuring products meet global safety standards and prevent toxic metal exposure from consumer goods.

Objectives and Study Overview

This application note describes two complementary calibration approaches—external calibration and isotope dilution mass spectrometry (IDMS)—using an Agilent 7500ce ICP-MS to measure Cd, Cr, Hg and Pb in plastics following microwave-assisted acid digestion. The goals were:

• Validate external calibration against IDMS as a confirmatory, SI-traceable method
• Estimate measurement uncertainties in accordance with ISO/GUM and Eurachem/CITAC guidelines
• Demonstrate method suitability for RoHS compliance testing

Methodology

Plastic samples and certified reference materials (CRMs) were digested in nitric acid and hydrogen peroxide using a Multiwave 3000 microwave system. For external calibration, multi-element stock standards were prepared gravimetrically from NIST SRMs and diluted to cover expected analyte levels. IDMS employed enriched spikes (53Cr, 111Cd, 199Hg and 206Pb) to achieve a 1:1 isotope ratio in sample blends, using exact-matching double IDMS protocols. Signal drift was monitored by bracketing samples with blanks and mid-level standards in external calibration, and by alternating calibration blends with sample blends in IDMS.

Instrumentation Used

• Agilent 7500ce ICP-MS with Octopole Reaction System (ORS) and Integrated Sample Introduction System
• Glass concentric nebulizer and cooled Scott double-pass spray chamber (2 °C)
• Helium collision gas mode for Cr, standard mode for Cd, Hg and Pb
• Gold added to rinse and internal standard to improve mercury washout

Main Results and Discussion

External calibration and IDMS delivered closely matching concentrations in an interlaboratory comparison sample (~252–254 µg/g Cr, ~36 µg/g Cd, ~392–400 µg/g Hg, ~460–470 µg/g Pb). Expanded uncertainties (k=2) for external calibration ranged from 8–42 µg/g, while IDMS uncertainties were generally lower (1–19 µg/g). Quality control recoveries for CRMs and independent standards fell within 96–108% with overlapping uncertainty ranges. In an international study, LGC’s IDMS results agreed with the study median to within 1.3%, confirming method accuracy and interlaboratory comparability.

Benefits and Practical Applications

• External calibration on the Agilent 7500ce ICP-MS provides a rapid, cost-effective approach for routine RoHS compliance testing.
• IDMS serves as a robust SI-traceable confirmation technique, ideal for national metrology institutes and proficiency testing providers.
• Helium collision gas effectively removes 40Ar12C interference on 52Cr, enhancing measurement reliability without chemical separation steps.

Future Trends and Opportunities

Advances in collision and reaction cell technology will further reduce polyatomic interferences, enabling lower detection limits for regulated elements. Development of certified matrix-matched reference materials and automation of IDMS workflows could expand traceability services to a broader range of polymers and complex matrices. Integration of high-throughput sample introduction systems will support increased laboratory productivity for compliance and quality control.

Conclusion

The study demonstrates that external calibration on an Agilent 7500ce ICP-MS, validated by isotope dilution, yields accurate and precise quantification of Cd, Cr, Hg and Pb in plastics. Both calibration strategies meet RoHS testing requirements, with IDMS providing the ultimate benchmark for traceability and external calibration offering an efficient solution for routine analysis.

References

1. Directive 2002/95/EC on restriction of hazardous substances in electrical and electronic equipment
2. ISO Guide to Expression of Uncertainty in Measurement, ISO, Geneva, 1995
3. Eurachem/CITAC Guide: Quantifying Uncertainty in Analytical Measurement, 2nd Edition, 2000
4. Catterick et al., J. Anal. At. Spectrom., 1998, 13, 1009
5. Hearn et al., Metrologia, 2008, 45, 08001
6. Goenaga-Infante et al., Anal. Bioanal. Chem., 2008, 290, 629
7. Santamaria-Fernandez et al., J. Anal. At. Spectrom., 2006, 21, 413
8. Turner, Agilent ICP-MS Journal, 2007, 30, 6