Ottimizzazione e validazione di un protocollo basato sulla Pirolisi-GC/MS per l'identificazione e la quantificazione di undici tipi di microplastiche

Plastic pollution is a major environmental issue caused by the accumulation of plastic waste in natural ecosystems. Microplastics (MPs) are a ubiquitous class of contaminants which have received significant attention because of their potential harmful effects on ecosystems and human health. In recent times, several analytical techniques were exploited for MPs analysis, with pyrolysis followed by gas chromatographic analysis that was proven to be a valuable technique for the identification and quantitation of MPs. In this regard, the purpose of this thesis work was the optimization and validation of a Pyrolysis (Pyr)-GC/MS based protocol for the identification and quantitation of 11 types of microplastics (polypropylene PP, polyethylene PE, polyethylene terephthalate PET, nylon-6 N6, nylon-6,6 N66, polyvinyl chloride PVC, polycarbonate PC, polymethyl-methacrylate PMMA, polystyrene PS, styrene-butadiene copolymer SB, acrylonitrile-butadiene-styrene copolymer ABS) in environmental samples. An internal standard (anthracene-d10) was used through all the study. The optimization of the main GC-parameters (heating ramp and injection temperatures) was obtained in order to achieve the optimal signal-to-noise ratio (normalized by the sample mass). Optimized conditions (injection T = 320°C; heating ramp T = 15°C/min) were used to register the pyrograms of the 11 target micropolymers and each MS spectrum was correctly attributed to its relative MPs, thus creating a user library to be exploited for a subsequent fast detection of the different types of polymers. Furthermore, a series of characteristic pyrolytic compounds and their respective m/z, necessary for the identification and quantification of unknown MPs, have been identified using the total ion pyrogram. Calibration curves over 10 levels were built for all the tested polymers, using a certificate standard mix that was diluted with SiO2 as solid diluent. The instrumental response was obtained using SIM of preselected indicator ions related to characteristic pyrolyzates. Excellent linearity (from R2 = 0,9927 for PC to R2 = 0,9993 for PE) was obtained for all polymers over 2 orders of magnitude, even up to 3 orders for SB, PS and ABS. Limits of detection (LOD) were also correctly calculated testing some of the most used approaches, in order to evaluate which best fits the optimized protocol. Results were in the mass range 0,002 µg (PS) – 3 µg (PE). The LOD calculated for PMMA, SB, PS, N6 and ABS are lower compared to what is reported in the literature. The trueness and the precision of the method were determined to describe the accuracy of the measurements and therefore to evaluate the performance of the analytical method. Trueness was tested by analyzing the standard mix of known concentration, and the results showed a relative error (Erel%) < 20% for 7 polymers (N66, PP, PC, N6, PE, PS, ABS). Precision was evaluated by performing replicate measurements on the same objects. Repeatability was found to be good with RSD% lower than 20% for all tested polymers. Subsequently, these measurements were also conducted on real MPs (PP and PP) with positive results for PE (RSD% = 12%; Erel% = 2.5%). Finally, the optimized Pyr-GC/MS based protocol was applied for the quantitation of MPs in fortified soil samples, that were extracted following a previously developed protocol.