Unravelling the Particle Size Effect and Standard Selection on Pyrolysis-Gas Chromatography-Mass Spectrometry Quantification: A study of Polystyrene

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.