Improved Reliability of Raman Spectroscopic Imaging of Low-Micrometer Microplastic Mixtures in Lake Water by Fractionated Membrane Filtration

Low-micrometermicroplastics (LMMPs), typically in the size range,1-10 mu m, are emerging contaminants ubiquitously presentin aquatic systems. However, the quantification of LMMP mixtures inenvironmental waters is hindered by the limitations of current analyticalmethods. In this study, we developed a novel analytical method thatcouples a fractionated membrane filtration with Raman microspectroscopy(mu-Raman) to reliably quantify LMMPs in lake water. The fractionatedmembrane filtration system recovered >90% of the mixed polystyrene(PS) and poly(methyl methacrylate) (PMMA) LMMPs (i.e., 1.5, 3, 5,and 8 mu m) from water. By separating LMMPs into 1-5 and5-10 mu m size fractions, the quality of the Raman imagesof small LMMPs (i.e., 1.5 and 3 mu m particles) acquired directlyon the membrane filters improved substantially. The reliability ofLMMP Raman imaging was further improved by tracking the sum and productof their three characteristic Raman bands. In this way, the interferentRaman signals from the lake water matrix and membrane filters weresignificantly suppressed. This method provides a reliable tool torecover, separate, and quantify LMMP mixtures in complex water matrices,paving the way toward a deeper understanding of their environmentalimplications. This study reports a reliable analyticalmethod that canquantify a complex mixture of low-micrometer microplastics in lakewater.