Variable-Depth Surface Composition Measurements of Micro- and Nano-Plastics Using Matrix Assisted Laser Desorption Ionization (MALDI) Mass Spectrometry

SAMANTHA KRUSE, Andre Benally, Mohammad Shohel, Steven Storch, Jake Zenker, Andres Sanchez, Jess Kustas, Ryan Davis, Sandia National Laboratories

     Abstract Number: 180
     Working Group: Chemicals of Emerging Concern in Indoor and Outdoor Aerosol: Sources, Vectors, Reactivity, and Impacts

Abstract
Micro- and nano-plastics (MNPs) are an emerging environmental contaminant that can persist in the atmosphere for days to weeks due to their increasingly small sizes. Aerosolized MNPs have been identified in samples across the globe, with higher concentrations near large cities and industrial sources, and lower concentrations as far remote as the arctic. MNPs are known to adsorb pollutants while in the environment, which can exacerbate their impacts on the environment and public health. As MNP concentration in the atmosphere increases, it becomes critical to better understand the unique surface chemistry of MNPs. To approach this problem, we are developing a technique to analyze the surface composition of MNP using soft ionization mass spectrometry. In this approach, aerosolized MNP are coated with an organic matrix using a custom-built saturator/condenser apparatus and collected on a substrate for analysis with matrix-assisted laser desorption ionization mass spectrometry (MALDI). We demonstrate the application of this approach with polystyrene latex (PSL) spheres. The coated PSL spheres were collected by a micro-orifice uniform deposition impactor (MOUDI), and their matrix coating thickness was determined in real time by an aerodynamic particle sizer (APS). Post-collection, the samples were measured using atomic force microscopy (AFM), scanning electron microscopy (SEM), and MALDI to determine their surface morphology and composition. The depth of the measurement into the surface of the PSL spheres were determined by the ratio of matrix and polystyrene signal. The influence of different variables including matrix type, coating thickness, and PSL sphere diameter will be discussed.

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