In this study, the analytical reliability of the thermo-analytical technique of pyrolysis coupled with gas chromatography (Py-GC-MS) was evaluated for the identification and quantification of eight common microplastics (MPs) in aqueous matrices of varying complexity. Depending on the filtration rate of the matrices, two different sample pre-treatment protocols were developed, dividing the samples into (i) low complexity, which were filtered at 0.7 µm using glass fibre filters, and (ii) high complexity, which were subjected to a microwave-assisted digestion process using hydrogen peroxide as a reagent. The low complexity matrices analysed in this study included mineral water in polyethylene terephthalate (PET) bottles (BMW), demineralised water (DMW), tap water (TW) and water further treated with activated carbon and distributed in public drinking fountains (FOW). The highly complex matrices included wastewater (WW) from primary sedimentation (PS), biological oxidation (BO), clarification-flocculation (CL) and quaternary treatment (QT).
In all WW samples examined, digestion significantly accelerated the filtration process. Although in a limited number of cases the matrix effect |ME%| was >30%, microwave-assisted digestion provided less evidence of an improvement in ME%. The apparent recovery values in DMW and DW samples were higher than those in WW-BO (67±19) and showed a very similar distribution (90±24 and 87±25, respectively). Based on the 12 criteria of the Green Analytical Chemistry, the greenness of the new methods was evaluated using AGREE [1], obtaining scores higher or comparable to previously published Py-GC-MS procedures. In particular, our approach and most of the studied protocols showed comparable and rather high scores for low complexity samples (0.53-0.56). High complexity matrices presented lower greenness values (0.19-0.43) due to the more elaborate protocols to which they are subjected. Poly(methyl methacrylate) and PET were never detected, while different levels of contamination were found for polyethylene, polyvinyl chloride, polycarbonate, polystyrene, polypropylene, and polyamide. The lowest contaminations were found in BMW and DMW. FOW was more contaminated than TW (five MPs detected at 2.7-138 µg/L vs. two MPs at <0.62-23 µg/L). Concentrations in WWs were in the order QT<CL<PS<<BO.
Pena-Pereira F., Wojnowski W., Tobiszewski M., Analytical Chemistry, 92 (2020), 10076–10082. https://doi.org/10.1021/acs.analchem.0c01887