A Simple Sample Preparation Method to Significantly Improve Fourier Transform Infrared (FT-IR) Spectra of Microplastics

Abstract

Spectroscopic analysis has become an essential part of the rapidly growing field of microplastic (MP) research. Here we introduce a simple sample preparation method which dramatically improves results from Fourier Transform Infrared (FTIR) analysis of MP and other environmental fibres. Our method provides cost-effective, reliable, high-quality spectra that achieve high-matching scores to polymer libraries. The efficacy of this method is demonstrated with two environmental datasets from Singapore and Phnom Penh that were collected while sampling for atmospheric MPs. The method developed and applied in this study is a simplification of the KBr method, where the analysed fibre is pressed to a thickness of <10 μm, however no KBr powder is required. For the combined dataset, 379 non-pressed fibres were analysed with 193 (51%) returning a Search score of ≥80% (chosen minimum Search score threshold), and 259 pressed fibres, with 254 (98%) returning a Search score of ≥80%. Direct comparisons of fibres before and after pressing show that the highest individual Search score, and average Search score from multiple single-point measurements, are overwhelmingly higher following our method. Our method immobilises and improves the surface of the fibre, by creating a wider and uniform area for measurements to be taken. For FTIR operators, this saves considerable time, improves reliability of the analysis, and importantly, provides reproducibility of the spectra generated.

Man-made natural and regenerated cellulosic fibres greatly outnumber microplastic fibres in the atmosphere

“…The term "regenerated cellulosic fibres" refers to rayon microfibres, , although rayon may have other names including "cellophane," "modal," "lyocell," or "viscose" (Athey and Erdle, 2021;Shen et al, 2010;Tobler-Rohr, 2011). We group these together as natural and regenerated cellulosic microfibres are chemically very similar, and are difficult to distinguish using common chemical identification techniques (Comnea-Stancu et al, 2017;Finnegan et al, 2022). We compare cellulosic microfibres to microfibres that have a petrochemical origin, which are typically dominated by polyester (polyethylene terephthalate -PET) or nylon (polyamide -PA).…”

Application of Infrared and Near-Infrared Microspectroscopy to Microplastic Human Exposure Measurements

“…Finnegan et al proposed using the KBr pellet method, but without powder, to press individual particles to a thickness <10 µm. 103 This sample preparation method, whereby pressed particles remain on the surface of two stainless steel dies, substantially improved the hit quality indices of particles, from 51% to 98% having an HQI > 80%. 103 Whether this technique could be applicable to small particle sizes by pressing the die onto particulates, rather than manually transferring individual particles, remains to be tested.…”

Polymer Characterization of Submerged Plastic Litter from Lake Tahoe, United States

“…When comparing the match percent from pristine polymers to each litter subsample (Table S3, Supplemental Material), PVC showed the lowest percent match followed by PA6/PA66. This may be a result of degradation, the addition of fillers and additives, or incomplete contact with the diamond crystal during measurement because of curved, irregular, or nonmalleable subsamples, as these factors can affect the match 53,54 as has been previously shown for PVC identification with Fourier transform infrared spectroscopy (FT-IR). 55 Additionally, the high number of unknown polymers (23.1%, n = 119) is potentially a result of the factors listed above, or a function of the limits of the available reference spectra library.…”