Development of a DART-HRMS Method to Characterize Chemical Composition of Microplastic Particles

EMILY HALPERN, Christopher P. West, Alexander Laskin, Purdue University

     Abstract Number: 298
     Working Group: Instrumentation and Methods

Abstract
As the global demand for plastic grows, plastic pollution has become more of an environmental concern. Microplastics are released from plastic waste that is left to degrade and it proliferates in the air, organisms, water systems, and soil. To determine the ecotoxicological impact of microplastics, a comprehensive, untargeted method of determining their chemical composition is needed. Here we investigate direct analysis in real-time high-resolution mass spectrometry (DART-HRMS) and pyrolysis DART-HRMS (pyro-DART-HRMS) methodologies as an analytical workflow to study chemical composition of plastic standards and mixed waste plastic. DART allows for ambient and rapid ionization of solid and liquid samples with no sample preparation, while pyro-DART allows for thorough polymer description with high desorption temperatures and temperature-based separation of compounds. Kendrick mass defect analysis is used to simplify the complexity of polymer spectra and identify characteristic CH₂-H₂ fingerprints for plastic types to allow for their distinction in mixed waste. By first analyzing common plastic standards, a spectral library of common plastics was first constructed. This spectral library is then applied for the deconvolution of mixed microplastic samples. Further contaminant identification is facilitated with high-resolution mass spectrometry, which allows for identification of nitrogen, sulfur, and oxygen containing contamination in plastic samples. Chlorine and bromine containing organic species were detected through their characteristic isotope distributions. The analysis of these common organic pollutants allows for assessment of the contamination risk of these microplastic sources. Mixed microplastics contain high amounts of N, O, S, Cl, and Br contamination which increase their pollution potential. This work demonstrates a new analytical method for fast and comprehensive characterization of mixed microplastics.