Novel calibration approach for particle size analysis of microplastics by Laser Ablation Single Particle-ICP-MS

The need to analyze and characterize microplastics (MPs) is ever-increasing to monitor and understand their environmental impact. In this work, a developed calibration approach that utilizes an in-house-created polystyrene (PS) thin film for the sizing of MPs is presented, circumventing the need for certified particulate standard material. LA was used for sampling and transporting intact MPs of different sizes and polymer types to the ICP-MS. For the calibration, defined amounts of carbon were introduced into the ICP-MS by quantitatively ablating a polymer thin film with different laser spot sizes. With this approach, a LOD of 4.85 pg carbon was obtained, which translates to a size of 2.12 μm for spheric PS particles. The calibration using PS thin film was successfully applied to sampled PS MPs and allowed accurate sizing of 2 μm, 3 μm, and 4.5 μm particles. When using the PS calibration for determining polyvinyl chloride (PVC) and poly(methyl methacrylate) (PMMA) particle sizes, a good estimate of the size could be achieved despite the different compositions of the polymers. This indicates the universal applicability of the presented approach. The investigation of the transport efficiency showed that it is mainly influenced by particle size, and factors such as the polymer type and length of the transport line and carrier gas. Under optimum conditions, up to 95% of the sampled particles were detected.