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Unravelling the particle size effect and standard selection on pyrolysis-gas chromatography-mass spectrometry quantification: A study of polystyrene
Summary
Scientists rely on a common lab technique to measure how much plastic (specifically polystyrene, used in items like foam cups and food containers) is present in environmental and food samples, but this study found that the calibration method used can throw off results by 64-78%, meaning we might be over- or under-counting how much microplastic is actually there. Using a special reference chemical to correct for this error helped reduce the mistake, but didn't fully fix it—highlighting that as scientists work to understand how much plastic we're exposed to and what it means for our health, we need better, more standardized testing methods to get accurate answers.
The increasing detection of micro- and nanoplastics in the environment has raised the need for reliable and standardized analytical methods. Among the available techniques, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) is widely applied since it is a powerful technique for both microplastic identification and quantification using polymer-specific markers. However, the quantification accuracy is still challenged by the sample type, and matrix interferences. In this study, calibration approaches were evaluated for polystyrene (PS) using aqueous polymer suspensions and a commercially available microplastic (MP) calibration mixture. For PS, calibration curves did not exhibit any differences correlated with the particle size. However, the MP mixture consistently produced higher styrene trimer signals due to contributions from styrene-containing copolymers and suspected decreased pyrolysis efficiency, leading to a PS quantification error of 64 % to 78%. The use of poly(4-fluorostyrene) as internal standard reduced these discrepancies, reducing the quantification error up to 31% for higher masses (1.25 µg), but did not completely eliminate them. These findings highlight the need to carefully consider the calibration type and the use of an internal standard when establishing calibration protocols for micro- and nanoplastic quantification by Py-GC-MS, as inappropriate calibration approaches may lead to substantial quantification bias, particularly when analyzing small particles where heat transfer effects can impact the pyrolysis process.