Monitoring Heavy Metals by ICP- OES for Compliance with RoHS and WEEE Directives

Importance of the Topic

Electronic and electrical equipment production has expanded rapidly, generating large volumes of waste electrical and electronic equipment (WEEE). Most WEEE ends up in landfills, releasing hazardous heavy metals into the environment. To protect human health and comply with global regulations such as RoHS and WEEE directives, routine monitoring of restricted metals in plastic components is essential.

Objectives and Overview

This study evaluates sample preparation and analytical protocols for determining cadmium (Cd), lead (Pb), chromium (Cr) and mercury (Hg) in polymer matrices using inductively coupled plasma–optical emission spectrometry (ICP-OES). The goal is to identify robust methods that meet the stringent concentration limits imposed by RoHS (100 mg/kg for most metals, 1000 mg/kg for Pb, Cr, Hg; 100 mg/kg for Cd).

Methodology and Instrumentation

Sample preparation methods compared include:

• EN 1122 H₂SO₄/H₂O₂ wet digestion (Cd only).
• Open HNO₃/H₂O₂ digestion.
• Microwave-assisted digestion (EPA Method 3051A) using HNO₃.

Reagents of analytical grade and matrix-matched calibration standards ensured accuracy. Two certified reference materials (ERM-EC 681 polyethylene and NMIJ CRM 8102a ABS resin) were analyzed to validate recoveries. Instrumentation comprised an Agilent 710-ES axial ICP-OES with echelle polychromator and CCD detector, operated at 1.2 kW plasma power, 15 L/min plasma gas flow, and standard sample introduction conditions.

Main Results and Discussion

Detection limits for Cd, Pb, Cr and Hg by ICP-OES were well below RoHS thresholds. Open HNO₃/H₂O₂ digestion provided accurate results for Cd, Pb and Cr but suffered Hg losses due to volatilization. EN 1122 delivered reliable Cd values but is unsuitable for Pb and Cr. Closed-vessel microwave digestion achieved full recoveries for all four metals, with measured concentrations in close agreement with certified reference values.

Benefits and Practical Applications

The optimized microwave digestion coupled with ICP-OES offers a fast, multi-element approach ideal for quality control laboratories tasked with regulatory compliance testing of electronic plastics. It minimizes sample handling, reduces contamination risk, and delivers reproducible results at low detection limits.

Future Trends and Potential Applications

Emerging global regulations will drive demand for even lower detection limits and higher throughput. Integration with ICP-MS or automated sample preparation systems, combined with screening techniques such as XRF, can further enhance efficiency. Broadening applications to other polymer additives and flame retardants will support comprehensive safety assessments.

Conclusion

Microwave-assisted acid digestion paired with ICP-OES provides a robust, sensitive and compliant method for quantifying Cd, Pb, Cr and Hg in plastic materials. This protocol meets RoHS/WEEE requirements and is suitable for routine monitoring in manufacturing and environmental laboratories.

References

1. Realff MJ, Raymond M, Ammons JC. E-Waste: an opportunity. Materials Today. 2004;40–45.
2. Hilty LM. Electronic waste – an emerging risk? Environ Impact Assess Rev. 2005;25:431–435.
3. Widmer R, Oswald-Krapf H, Sinha-Khetriwal D, Schnellmann M, Boni H. Global perspectives on e-waste. Environ Impact Assess Rev. 2005;25:436–458.
4. Darby L, Obara L. Household recycling and disposal of electrical and electronic equipment. Resour Conserv Recycl. 2005;44:17–35.
5. European Parliament and Council. Directive 2002/95/EC on restriction of certain hazardous substances in electrical and electronic equipment. OJ L 37/19. 2003.
6. European Parliament and Council. Directive 2002/96/EC on waste electrical and electronic equipment. OJ L 37/24. 2003.
7. California State Legislature. Electronic Waste Recycling Act of 2003 (SB 20, SB 50).
8. Hicks C, Dietmar R, Eugster M. The recycling and disposal of electrical and electronic waste in China—legislative and market responses. Environ Impact Assess Rev. 2005;25:459–471.
9. Franklin R. China RoHS and China WEEE. 2005.
10. Japan Green Procurement Survey Standardization Initiative. Guidelines for the Management of Chemical Substances in Products. 2005.
11. Ernst T, Popp R, van Eldik R. Quantification of heavy metals for the recycling of waste plastics. Talanta. 2000;53:347–357.
12. Ritter A, Michel E, Schmid M, Affolter S. Interlaboratory test on polymers: determination of heavy metals. Polymer Testing. 2004;23:467–474.
13. EPA Method 3060A. Alkaline Digestion for Hexavalent Chromium. 1996.
14. EPA Method 7196A. Chromium, Hexavalent (Colorimetric). 1992.
15. EPA Method 8082. Polychlorinated Biphenyls by Gas Chromatography. 1996.
16. EPA Method 8270C. Semivolatile Organic Compounds by GC/MS. 1996.
17. Brittain R. Fast, sensitive determination of polybrominated diphenyl ethers by tandem MS. Varian GC/MS App Note No. 75. 2004.
18. Wolska J. Elemental analysis in the plastic industry. Plast Addit Comp. 2003;50–55.
19. Institute for Reference Materials and Measurements. ERM-EC 681 Polyethylene.
20. National Metrology Institute of Japan. CRM 8102a ABS resin.
21. European Standard EN 1122. Plastic—Determination of Cd—Wet decomposition method. 2001.
22. EPA Method 3050B. Acid digestion of sediments, sludge, and oils. 1996.
23. EPA Method 3052. Microwave assisted acid digestion of siliceous and organically based matrices. 1996.
24. EPA Method 3051A. Microwave assisted acid digestion of sediments, sludge, soils and oils. 1998.