Thermal fragmentation enhanced identification and quantification of polystyrene micro/nanoplastics in complex media

As an emerging field of study, microplastics have drawn tremendous attention, but until now little is known about their fate and impacts in the environment. A critical bottleneck is lack of reliable techniques to identify and quantify microplastics in complex media. Here we present a simple, rapid, and effective method for identification and quantification of micro/nanoplastics (MNPs) based on thermal fragmentation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with polystyrene (PS) particles as a model MNP. The PS MNPs are identified by fingerprint peaks in both low-mass (m/z 90, 104, 128, 130, and 312-318) and high-mass regions (repeated peaks with Δm/z 104 in the m/z range 350-5000), and the quantification is carried out with m/z 315.3. The different ionization behaviors enable the differentiation of MNPs with different molecular weights. Notably, we find that a simple thermal pretreatment at 380 °C can facilitate the fragmentation of PS and significantly enhances the intensities of fingerprint peaks in low-mass regions, yielding a detection limit of 25 ng for PS MNPs. The applicability of the method in different sample matrices and for other types of MNPs such as polyethylene terephthalate (PET) is also validated. Considering the current shortcomings in MNP analysis, this work provides a powerful tool to advance the MNPs research.