Extending the Linear Dynamic Range of Single Particle ICP-MS for the Quantification of Microplastics

In response to the growing concern of microplastics (1 μm to 5 mm) accumulation affecting human health, the development of analytical methods continues to be critical for the detection and characterization of microplastic particles. In this context, pursuing exceptional particle detection capability down to practical low levels and rapid analyses with high sample throughput makes single particle inductively coupled plasma mass spectrometry (spICP-MS) very attractive for microplastics analysis. Existing spICP-MS-based studies have routinely shown limitations in the accurate sizing and quantification of particle number concentration through targeting carbon content, with reported size limits of detection in the range of 0.62 to 1.8 μm and a substantial reduction in the transport of particles larger than 3 μm. In this work, the linear dynamic range of spICP-MS for the accurate quantification of polystyrene microparticles (PS MPs) via the monitoring of their carbon content (¹³C⁺) is extended to larger particle sizes (5 μm) through using a high efficiency sample introduction system with rigorous optimization of the ¹³C signal and operating at a lowered nebulizer gas flow to improve sample transport of larger particles to the plasma. Reliable quantification of particle number concentration (PNC), accepted as falling within 20% of expected particle stock concentrations, was achieved through a 20% lowered nebulizer gas flow for a full suite of commercial PS MPs ranging from 2 to 5 μm as well as a 2.2 and 4.8 μm PS MP contained within mixtures of the two materials, regardless of PNC ratio.