A New Strategy for Confident Characterization of Extractables from Post- consumer Recycled Plastics Using LC-QTof

Significance of the Topic

Modern society relies heavily on plastic materials across various applications. Recycling post-consumer plastics not only conserves fossil resources but also mitigates environmental pollution. Ensuring that recycled low density polyethylene (rLDPE) matches the performance and safety profile of virgin material requires comprehensive chemical characterization of extractable impurities.

Study Objectives and Overview

This study introduces an untargeted discovery workflow combining liquid chromatography and high-resolution time-of-flight mass spectrometry to differentiate and profile extractable compounds in various batches of rLDPE, ranging from virgin to low- and high-quality recycled samples. Key marker compounds are identified to assess material quality and safety.

Methodology

• Sample Preparation: Methanol extraction (15 g pellets or 2.5 g fluff, 100 mL, 40 °C, 1 h), followed by filtration and QC pooling.
• LC Conditions: Reverse-phase separation on a CORTECS C18 column (2.1×100 mm, 1.6 µm) at 50 °C with a water/acetic acid–methanol gradient and 0.3 mL/min flow.
• MS Conditions: Xevo G3 QTof in ESI positive/negative modes using HDMSE acquisition, lock mass calibration, and collision energy ramps.
• Data Processing: Peak picking, alignment, and normalization performed in Progenesis QI, followed by statistical filtering (p≤0.05, CV<30%, fold change>10×) and multivariate analysis (PCA, correlation clustering).

Applied Instrumentation

• Waters ACQUITY Premier LC System
• Xevo G3 QTof Mass Spectrometer
• CORTECS C18 Column (90 Å, 2.1×100 mm, 1.6 µm)
• MassLynx v4.2 and Progenesis QI 3.0 Software

Key Results and Discussion

A total of over 13 800 features in positive mode and 7 950 in negative mode were detected. PCA clearly separated virgin, good-quality, and poor-quality rLDPE in the positive mode. Correlation analysis highlighted clusters of compounds elevated in low-quality rLDPE. Annotation against FCCdb and CPPdb identified 33 marker compounds in poor-quality and 57 in both recycled grades, notably di-isononyl phthalate (DINP), di-isobutyl phthalate (DIBP), di-n-octyl phthalate (DNOP), and oleamide. Level 1 confirmation was achieved by matching standards’ retention times and MS/MS spectra.

Benefits and Practical Applications

• Rapid fingerprinting of recycled plastic batches to distinguish quality grades.
• Confident identification of safety-relevant chemicals using accurate mass and HDMSE fragmentation.
• Streamlined workflow for quality assurance in recycling and regulatory compliance.

Future Trends and Potential Applications

Advances may include automated high-throughput screening for non-intentionally added substances, expansion to other polymer types, integration with quantitative MS/MS assays, and real-time monitoring of recycling streams for quality control.

Conclusion

The presented LC–QTof discovery workflow effectively discriminates rLDPE quality by profiling extractable compounds. Identification of key phthalate markers supports robust quality assessment and safety evaluation of recycled plastics.

References

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