Multimethod Platform Based on Dynamic Image Analysis and spICP-MS for Number-Based Quantification of Microplastics

A multimethod platform based on the combination of dynamic image analysis (DIA) and single particle inductively coupled plasma mass spectrometry (spICP-MS) has been developed, validated, and applied for the first time to reliably determine the particle number concentration of small microplastics. The ability of the DIA/spICP-MS platform to reliably detect and quantify microplastics was carefully studied using polystyrene (PS) microparticles in the size range from 1 to 10 μm. Critical instrumental parameters affecting the accuracy of the number-concentration measurements were identified for both techniques. In the case of DIA, the detection threshold (DT) was found to be the most important, while for spICP-MS, both the calibration of the transport efficiency (TE) using the frequency method and the choice of sample introduction system were critical. Under optimal conditions, the number-concentration values obtained for 5 μm PS-Latex microspheres using DIA and spICP-MS methodologies agreed well within their associated uncertainty (u, k = 1 of approximately 2.5% for DIA and u, k = 1 of approximately 10.2% for spICP-MS). Main contributing factors to the overall measurement uncertainty were evaluated for methodology based on both techniques, being the variability in the number of detected particles for DIA and the number of detected particles and transport efficiency calibration for spICP-MS. These accounted for approximately 94% (DIA) and approximately 45% (spICP-MS) of the overall uncertainty budget, respectively.