Analysis of Plastic

Importance of the Topic

Plastic materials are ubiquitous in consumer and industrial applications, yet they can contain trace levels of toxic metals such as lead, cadmium, mercury and chromium. Accurate determination of these contaminants is critical to ensuring product safety, meeting regulatory requirements and protecting environmental and human health. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) provides rapid, multi-element screening with high sensitivity, making it ideal for quality control and compliance testing in the plastics industry.

Objectives and Study Overview

This study evaluates three sample decomposition techniques—dry-ashing, wet decomposition and microwave digestion—combined with a multi-type ICPE-9000 ICP emission spectrometer. It aims to quantify trace metals in polyethylene reference materials (BCR680, BCR681), compare method performance, and assess agreement with certified values.

Methodology

Sample Preparation:

• Dry-Ashing: Shavings of resin are ashed at 450 °C in a furnace, treated with sulfuric and hydrochloric acids, then dissolved in nitric acid.
• Wet Decomposition: Samples are carbonized in a Kjeldahl flask using sulfuric, nitric acids and hydrogen peroxide, followed by repeated acid additions until clarity is achieved.
• Microwave Digestion: PTFE vessels loaded with nitric acid and hydrogen peroxide are heated under pressure for complete decomposition.

Analytical Conditions:

• Instrument: ICPE-9000 ICP Emission Spectrometer
• RF Power: 1.2 kW; Plasma Gas Flow: 10 L/min; Auxiliary Gas: 0.6 L/min; Carrier Gas: 0.8 L/min
• Sample Introduction: Nebulizer at 1.0 mL/min with a cyclone mist chamber; axial viewing mode

Used Instrumentation

• Shimadzu ICPE-9000 Multi-type ICP Emission Spectrometer
• Microwave Digestion System with PTFE Decomposition Vessels
• Kjeldahl Flasks and Mantle Heater
• Electric Furnace and Quartz Crucibles for Dry Ashing
• Mini Torch Accessory

Main Results and Discussion

All three decomposition methods produced quantitation values that closely matched certified reference values for BCR680 and BCR681. Dry-ashing and microwave digestion delivered accurate measurements of cadmium and lead, while the Kjeldahl approach also quantified total chromium and mercury effectively. Microwave digestion achieved reliable results for all target elements, with detection limits as low as 0.02 mg/kg for cadmium. Calibration curves exhibited excellent linearity (correlation coefficients near unity), confirming method robustness.

Benefits and Practical Applications

• High sensitivity and low detection limits ensure compliance with stringent regulations.
• Multiple digestion options accommodate a range of plastic matrices and additive levels.
• Rapid analysis and multi-element capabilities support routine QA/QC workflows.
• Microwave digestion reduces sample handling and contamination risk, improving laboratory safety and efficiency.

Future Trends and Opportunities

Future developments may include fully automated microwave digestion modules integrated with ICP-AES systems to streamline sample preparation. Advances in high-resolution spectrometers and enhanced detector technologies could further lower detection limits and expand the range of detectable elements. Additionally, chemometric calibration strategies and machine learning algorithms hold promise for correcting matrix effects and improving quantitation accuracy in complex polymer formulations.

Conclusion

The combination of appropriate sample decomposition techniques and the ICPE-9000 spectrometer provides a reliable, high-throughput solution for trace metal analysis in plastics. Microwave digestion, in particular, offers superior performance in terms of sensitivity, accuracy and operational efficiency, making it the preferred choice for routine monitoring and regulatory compliance.

Reference

• US EPA SW-846 Method 3052
• BS EN 1122 Method A: 2001
• Food Hygiene Test Guidelines, 2005 Physics and Chemistry, Ministry of Health, Labor and Welfare