Abstract: Marine microplastics have emerged as critical pollutants, attracting significant attention in marine scientific research. However, the complex and high-salinity seawater matrix poses substantial challenges for their separation and detection. This study presents the membrane filtration-pyrolysis-mass spectrometry (MF-Eh-Pyr-MS) method, which integrates membrane filtration (MF) with electromagnetic heating pyrolysis-mass spectrometry (Eh-Pyr-MS) to enrich and detect micro- and nano-plastics in real seawater environments. Using polypropylene (PP), polyethylene (PE), and polystyrene (PS) as target microplastics, the study systematically explores the effects of salt solute types, salt concentrations, and microplastic properties (such as type and particle size) on the applicability of the proposed method. Scanning electron microscopy (SEM) was utilized to characterize the filter membranes before and after pyrolysis and following filtration of different solutes, further validating the method’s feasibility. The results indicate that, except for a 3.5% (mass fraction) magnesium chloride solution, other salt solutes and salinity levels have minimal impact on analysis outcomes. Real seawater samples collected near Weihai were used for practical validation, with recovery rates for plastics ranging from 32.8% to 104.8% across three sampling points. This work provides a straightforward and effective approach for the separation and detection of nanoplastics in seawater, offering valuable insights into marine micro- and nano-plastic research.

Key words: Pyrolysis-mass spectrometry, Microplastics, Seawater, Membrane filtration