Precision Analysis of Toxic Elements in Plastic by ICPE-9800 Series

Significance of Topic

Rapid and accurate determination of restricted toxic elements such as cadmium, lead, chromium, mercury and arsenic in polymeric materials is critical to comply with global regulations (RoHS, ELV) and ensure consumer safety. Analytical workflows that combine efficient sample preparation with high-throughput detection enable laboratories to meet tightening regulatory limits while controlling operating costs.

Objectives and Study Overview

This study evaluated and compared three sample digestion approaches for quantitative analysis of toxic metals in polyethylene standard materials (BCR680 and BCR681) using a multi-type ICP atomic emission spectrometer. The main goals were:

• Assess recovery and precision for each pretreatment: dry ashing, wet acid decomposition and microwave-assisted digestion.
• Demonstrate the performance of the Shimadzu ICPE-9800 series with a CCD detector for rapid multi-element analysis.

Methodology and Instrumentation

Sample Preparation Methods:

1. Dry Ashing: 0.2 g sample mixed with sulfuric acid in a quartz crucible, heated on a hot plate then ashed at 450 °C. Ash residue was dissolved in hydrochloric and nitric acids and diluted to 20 mL.
2. Wet Decomposition: 0.2 g in a Kjeldahl flask digested on a heating mantle with sulfuric acid, nitric acid and hydrogen peroxide at 300–350 °C until organic material was oxidized, then brought to volume.
3. Microwave-Assisted Acid Digestion: 0.2 g in a sealed microwave vessel with nitric acid and hydrogen peroxide, digested under pressure and cooled before dilution to 20 mL. For samples with high additives, hydrofluoric acid was added.

Applied Instrumentation:

• Shimadzu ICPE-9800 series ICP-AES with CCD detector.
• Mini torch for reduced plasma gas consumption.
• Eco mode for standby gas and power savings.
• Vacuum spectrometer eliminating purge gas requirements.
• Operating conditions: RF power 1.2 kW; plasma gas 10 L/min; auxiliary gas 0.6 L/min; carrier gas 0.7 L/min; axial observation; approx. 2.5 min per sample including rinse.

Key Results and Discussion

Detection limits for all elements were well below maximum permissible RoHS thresholds. Recoveries close to certified values were achieved as follows:

• Dry ashing provided accurate Cd and Pb quantitation but underestimated some volatile elements due to high-temperature losses.
• Wet decomposition yielded good results for Cd, Cr, Hg and As, with limitations for lead due to sulfate precipitation.
• Microwave digestion delivered accurate quantitation across all target elements with minimal loss or interference.

These findings highlight the importance of choosing a digestion protocol tailored to the element’s chemical behavior.

Benefits and Practical Applications

• High-throughput multi-element analysis (2.5 min/sample) irrespective of the number of wavelengths.
• Reduced running costs through low gas and power consumption features of the ICPE-9800.
• Flexible pretreatment options to suit diverse plastic matrices and target analytes.
• Reliable compliance testing for regulatory frameworks in electronics, automotive and consumer goods industries.

Future Trends and Opportunities

Advances in automated sample preparation, integration with hyphenated techniques (e.g., ICP-MS), and AI-driven data processing will further enhance sensitivity and reduce analyst intervention. Miniaturized digestion systems and green chemistry approaches are emerging to minimize reagent use and waste, extending applicability across new polymer types and complex composites.

Conclusion

Combining optimized sample pretreatment with the Shimadzu ICPE-9800 series enables accurate, fast and cost-effective quantitation of regulated toxic metals in plastics. While all three digestion methods can yield valid results, microwave-assisted acid digestion offers the most comprehensive recovery and operational simplicity for multi-element testing.

References

• BS EN1122 Method A: 2001, Plastics – Determination of Cadmium (Wet Decomposition Method).
• US EPA SW-846 Method 3052, Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices.