Studying the degradation of bulk PTFE into microparticles via SP ICP-MS: A systematically developed method for the detection of F-containing particles

Fluoropolymers, such as polytetrafluoroethylene (PTFE), have unique properties, which enable versatile applications in industry and make them useful for various consumer products. However, it is known that these polymers degrade over time and form small particles with possible implications for environment and health. Building on previous reports for the detection of Fluorine (F) via inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) using a Barium-based modifier, this study presents a design of experiments approach (DoE), which optimised plasma parameters, ion optics, mass filtering and collision/reaction cell conditions systematically. The resulting method was capable to detect micro-scaled PTFE particles and to determine number concentrations as well as size distributions. Validation was carried out in two steps: First, micro-scaled PTFE standards were characterised via microscopy and Raman spectroscopy and second, carbon-selective single particle (SP) ICP-MS was employed to corroborate results obtained via the F-selective method. The developed method has a high utility to characterise the degradation of bulk PTFE into microplastics, which was demonstrated in an environmentally focussed proof-of-concept study. Here, bulk PTFE material was stirred in simulated seawater under UV-light illumination for 6 days. After this incubation period a microplastic number concentration of 2.35 x 105 F-based particles per gram immersed bulk PTFE was detected. PTFE particles had a mean mass and size of 28 pg and 2.7 µm, respectively.