Comparison of the ability of UV-Vis and UPLC-Q-TOF-MS combined with chemometrics to discriminate recycled and virgin polyethylene

A growing attention is attracted to the use of recycled plastics as food contact materials, and its chemical safety research and discrimination approach are indispensable. In current study, ultraviolet-visible spectrometry (UVVis) and ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOFMS) were used to provide spectral and mass fingerprinting for polyethylene (PE). Coupling with chemometrics, two methods were developed to discriminate recycled and virgin PE. UV-Vis combined with chemometrics could be a more accessible, simpler and faster approach. 237-331 nm in UV spectrum was regarded as marker region selected by orthogonal partial least-squares discrimination analysis (OPLS-DA) and the accuracy of both calibration and validation set could reach 100% in linear discrimination analysis (LDA) based on this region. Besides, 2314 ions were detected by UPLC-Q-TOF-MS and processed by MS-DIAL. 48 candidate chemicals were identified, including ketone, esters, carboxylic acid, alcohols and phenols, amine, nitriles, aldehydes and others. Possible origins of these compounds could be classified as plastic, food, drug, cosmetics and pesticide related. Many of these compounds are highly toxic, especially pesticide related, indicating that recycling in closed loop or sorting by the recycled plastic articles is very necessary if the recycled PE is going to be used as food contact material.

Automated summary

This study used UVVis and UPLC-Q-TOFMS techniques combined with chemometrics to provide spectral and mass fingerprinting for PE, developing two methods to distinguish recycled and virgin PE. The UV-Vis combined with chemometrics proved to be a more accessible, simpler, and faster approach for discrimination. The UV spectrum region of 237-331 nm was identified as a marker region, while UPLC-Q-TOF-MS detected 2314 ions and identified 48 candidate chemicals, highlighting the importance of strict identification and classification when using recycled PE as food contact material.