Quantitative sizing of microplastics up to 20 µm using ICP-TOFMS

A fundamental study of four different sample introduction systems was carried out to evaluate the upper size limit of microplastics measured by inductively coupled plasma-time-of-flight-mass spectrometry (ICP-TOFMS). Three different, certified microplastic samples (PS, PMMA and PVC) within a size range of 3-20 µm in suspension were measured. In this study, no particles larger than 10 µm could be detected using pneumatic nebulization for sample introduction. However, we were able to extend the upper size limit to 20 µm by either using a falling-tube device or a vertical downwards-pointing ICP-TOFMS. Particle transport efficiencies could only be estimated and were within a range of 13% to 184%. The particle size was quantified by using dissolved citric acid (non-matrix matched) and agreed with reference values. The critical size values were 2.3 µm for PS, 2.4 µm for PMMA and 3.0 µm for PVC. Additionally, in the case of PVC, chlorine could also be detected and the critical size value was 3.9 µm based on the ³⁵Cl⁺ ion signal.