Direct Characterization of Halogen-Based Microplastics via Single-Event ICP-Mass Spectrometry in Negative-Ion Mode

Halogen-containing microplastics such as polytetrafluoroethylene (PTFE) and poly(vinyl chloride) (PVC) are analytically relevant targets, yet their selective characterization by ICP-MS remains challenging, particularly for fluoropolymers due to the limited formation of F+ in conventional positive-ion mode. Here we introduce negative-ion single-event ICP-MS as a direct strategy for particle-resolved characterization of halogen-containing microplastics by monitoring F- and Cl- on a quadrupole ICP-MS without plasma modifiers or proxy-ion chemistry. PTFE and PVC particle standards were used as well-defined model systems, with scanning electron microscopy (SEM) confirming particle morphology and size distributions. Key acquisition and instrumental conditions governing event detectability were systematically optimized, enabling reliable transient detection at a dwell time of 100 μs. Using a conventional spray-chamber configuration, size detection limits of 1.18 μm (PTFE) and 0.73 μm (PVC) were achieved, improving to 0.68 μm (PTFE) and 0.45 μm (PVC) with a high-efficiency sample introduction system. Quantification strategies for negative-mode operation, including external calibration and transport-efficiency-based workflows, were further assessed. Overall, this work establishes negative-ion mode single-event ICP-MS as a direct platform for fluorine- and chlorine-selective microplastic detection and sizing, expanding the analytical scope of particle-resolved microplastic analysis beyond indirect fluorine detection or carbon-based approaches.