Identification of Microplastics by Calcined Sand Assisted Ambient Laser Desorption Electrospray Ionization Mass Spectrometry

Abstract

Electrospray ionization (ESI) and laser desorption ionization (LDI) exhibit inherent limitations when applied as standalone ion sources for the mass spectrometric analysis of microplastics (MPs). Herein, we report an ambient laser desorption electrospray ionization mass spectrometry platform, CSAA-LESI-MS, using low-cost, readily available, and eco-friendly calcined sand as the matrix. This system achieves qualitative and quantitative identification of MPs with varied optical and physicochemical characteristics, including strongly and weakly light-absorbing, polar and nonpolar MPs. Efficient ionization of all analyzed polymers was achieved within 1.2 s, affording nanogram-level limits of detection (LODs) and limits of quantification (LOQs) with correlation coefficients (R2) all exceeding 0.98. Seven representative polymer classes, including polyethylene (PE), polypropylene (PP), polyamide 6 (PA6), poly(methyl methacrylate) (PMMA), poly(ethylene terephthalate) (PET), polylactic acid (PLA), and poly(oxymethylene) (POM), yielded abundant, well-resolved backbone-specific fingerprint spectra. A total of 15 suspected particles were further distinguished successfully by PPMC-based spectral matching against polymer reference libraries. The CSAA-LESI-MS method provides a versatile, economical, and precise ambient mass spectrometry approach feasible for environmental MP analysis.