Microplastics analysis: is direct inlet Py-GC/MS exploitable for a polymeric characterisation of atmospheric aerosol?
Creators: name: Gregoris, Elena
Publisher: name: Zenodo
Year: 2023
Subjects: airborne microplastics
Py-GC/MS
direct inlet
matrix interference
polymer detection

description: Microplastics are emerging pollutants of great concern since they are widely distributed in the environment. While the occurrence of microplastics was studied in marine and freshwaters, sediments, soil, and different classes of organisms, the atmosphere was somewhat understudied, although it can be the most significant transport pathway from mid to high latitudes. Pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) has been identified as a promising technique for MPs analysis in the environment; it is widely used for various environmental matrices, but it has rarely been employed in airborne MPs research (Fan <em>et al.</em>, 2022). In this work, we explored the possible applicability of Py-GC/MS for detecting polymers in aerosol filters without any preparative step, estimating the interference of organic aerosol in total suspended particulate (TSP) samples. In our opinion, assessing the matrix interference is essential to understand if an organic matter removal step is necessary for an effective qualitative analysis of the urban atmospheric aerosol. We developed the “organic aerosol baseline” (OAB), the first attempt to estimate the contribution to the polymer tracer areas of the organic material present in the atmospheric aerosol. Even if it constitutes only a part of the organic aerosol, we selected humic acid as the representative substance of organic matter for this assessment, as previously done in the literature (Okoffo <em>et al.</em>, 2020). OAB was calculated for polymer tracers, considering the typical amount of organic aerosol in TSP, in the period and area of sampling, starting from the pyrolysis of a known amount of humic acid. The following equation is proposed: OAB = A<sub>n</sub> ∙ OM ∙ PM ∙ V ∙ fr<sub>sample</sub> where A<sub>n</sub> is the average tracer normalised areas in the humic acid pyrograms; OM is the organic matter fraction in the aerosol; PM is the aerosol concentration; V is the sample volume; fr<sub>sample</sub> is the fraction of sampling filter introduced in the sample tube. Only pyrolysis products with an area above the OAB level are considered plastic tracers (Gregoris <em>et al.</em>, 2023). This new approach identified polyethylene, polypropylene, and polystyrene in TSP samples (AirFlowPUF, Analitica Strumenti; 0.3 m<sup>3</sup> min<sup>−1</sup>; 48h- and 72h-samples). The analysis by Micro-FTIR carried out on the same samples led to the identification of the same polymers and revealed the presence of other plastic, not detected by Py-GC/MS. The discrepancy between results obtained by the two techniques is reduced if the analysis is conducted on pure commercial dust (House SRM2585), leading to the hypothesis that the crucial point could be the little portion of the filter practically analysable by the pyrolyser, rather than the presence of the matrix. The direct analysis represents the ideal screening procedure for saving time, costs, and waste; this is even more convenient if considering that plastics are difficult to extract and require dedicated instrumentation. Since the interference level does not appear to be a major obstacle to polymer detection, this approach could be useful as a screening method to be applied before the application of time-consuming techniques, dedicated to quantification. This work has benefited from the infrastructural support of the Centre for Trace Analysis (CeTrA) through the project IR0000032 (ITINERIS), funded by EU - Next Generation EU, PNRR. Fan, W. Salmond, J.A., Dirks, K.N., Cabedo Sanz P., Miskelly, G.M. and Rindelaub J.D. (2022) <em>Environ Sci Technol </em><strong>56</strong>, 17556–17568. Gregoris, E., Gallo, G., Rosso, B., Piazza, R., Corami, F., Gambaro, A. (2023) <em>J Anal Appl Pyrol</em> <strong>170</strong>, 105903 Okoffo, E.D., Ribeiro, F., O’Brien, J.W., O’Brien, S., Tscharke, B.J., Gallen, M., Samanipour, S., Mueller, J.F. and Thomas K. V. (2020) <em>Sci Total Environ</em> <strong>715</strong>, 136924.