MASS SPECTROMETRY TOOLS FOR CONFIDENT DISCRIMINATION OF DIFFERENT QUALITIES OF POST-CONSUMER RECYCLED PLASTICS

Importance of the topic

Plastic pollution represents a persistent environmental challenge, as fossil‐fuel derived polymers can remain intact for decades or centuries. Transforming post‐consumer recycled plastics (PCR) into a valuable resource requires reliable quality and safety assessment methods. High‐resolution mass spectrometry (HRMS) coupled with liquid chromatography (LC) offers an unbiased, sensitive approach to characterize chemical signatures and impurity profiles in recycled materials.

Study objectives and overview

• Establish a flexible LC‐HRMS workflow to profile recycled low‐density polyethylene (rLDPE) of varying quality grades.
• Differentiate virgin LDPE, virgin LDPE with additives, and recycled LDPE (good and poor quality) via non‐targeted analysis.
• Identify marker compounds characteristic of poor‐quality rLDPE batches.

Methodology and sample preparation

Samples were grouped into virgin LDPE (vLDPE), virgin LDPE with additives (vLDPE+), good‐quality rLDPE, and poor‐quality rLDPE, each with three replicates. Pellets and fluff were extracted by submerging in 100% methanol at 40 °C under magnetic stirring, filtered, and stored at 4 °C. Quality controls (QCs) were prepared by pooling aliquots from all extracts, randomized, and injected throughout the sequence. Chromatographic separation employed a CORTECS C18 column (1.6 µm, 2.1×100 mm) at 50 °C with a water/acetic acid–methanol gradient and 0.3 mL/min flow.

Instrumentation

Analysis was performed on an ACQUITY™ Premier LC system coupled to a Xevo™ G3 QTof mass spectrometer. Electrospray ionization in positive and negative modes (ESI+/–) was used, with a mass range of m/z 50–1200, acquisition rate of 5 Hz, and HDMSE acquisition (0–40 eV ramp for ESI+, 20–50 eV for ESI–). Lock mass (leucine enkephalin) ensured mass accuracy. Data processing utilized MassLynx™ v4.2 for acquisition and Progenesis™ QI v3.0 for statistical analysis.

Main results and discussion

Data processing steps—including peak picking, adduct grouping, retention time alignment, normalization, and filtering—yielded 2318 features in positive mode and 877 in negative mode. Principal component analysis (PCA) distinctly separated vLDPE, vLDPE+, good rLDPE, and poor rLDPE. Correlation analysis revealed two clusters of compounds strongly associated with poor‐quality rLDPE. Among these, a feature at m/z 441.2978 (retention time 9.89 min) was annotated as [M+Na]+ of C24H38O4, corresponding to di‐isononyl phthalate (DINP). HDMSE fragmentation and comparison with an authentic standard achieved level 1 identification with mass accuracy ±0.56 ppm and matching spectra.

Benefits and practical applications

• Provides an integrated workflow for rapid discrimination of recycled polymer quality using LC‐HRMS.
• Enables routine screening of marker compounds to support PCR grading and compliance with safety standards.
• Supports circular economy goals by ensuring traceability and quality control in recycled plastic streams.

Future trends and potential applications

Extending this approach to other polymer classes (HDPE, PET, PP) and integrating non‐target screening with machine learning can enhance marker discovery. Advances in high‐throughput HRMS, data analytics, and open databases will facilitate broader adoption in industrial quality assurance, regulatory monitoring, and environmental impact studies.

Conclusion

An unbiased LC‐HRMS workflow effectively distinguished quality grades of rLDPE and identified key marker compounds characteristic of poor‐quality recycled material. The combined use of HDMSE acquisition and multivariate analysis supports confident compound identification and offers a robust tool for PCR quality control.

References

1. Groh K J, Geueke B, Martin O, Maffini M, Muncke J. Overview of Intentionally Used Food Contact Chemicals and Their Hazards. Environ Int. 150:106225 (2021).
2. Groh K J et al. Overview of Known Plastic Packaging-Associated Chemicals and Their Hazards. Sci Total Environ. 651:3253–3268 (2019).
3. Schymanski E L et al. Non-target Screening With High-Resolution Mass Spectrometry: Critical Review Using a Collaborative Trial on Water Analysis. Anal Bioanal Chem. 407:6237–6255 (2015).