DEVELOPING SINGLE PARTICLE ICP-MS AS A TECHNIQUE TO ADVANCE MICROPLASTICS ANALYSIS CAPABILITIES

Abstract

Microplastics (1μm to 5 mm) are an emerging pollutant whose environmental accumulationcontinues to raise concerns over the potential impacts on human health. In response to this growing concern, the development of analytical methods continues to be critical for the detection and characterization of microplastic particles. Single particle inductively coupled plasma mass spectrometry (spICP-MS) has become very attractive for microplastic analysis under this context for exceptional particle detection capability (down to truly environmentally relevant levels), rapid analysis times, and high sample throughput. Existing microplastics work using spICP-MS has focused on the measurement of plastic particles through dopants or other functionalized particles. However, detecting plastics through carbon signatures remains challenging and limited. The work performed in this dissertation aims to address some of these challenges and limitations which include, poor microplastic particle transport in ICP systems for particles larger than 2 μm – 3 μm and the lack of metrological traceability between microplastic particles and existing metallic nanoparticle calibration standards. These issues were investigated from a fundamental analytical and metrological standpoint to advance the chemical analysis of microplastics. Initially, the adaptation of commercial instrumentation was required in order to enable the detection of any microplastic particle using spICP-MS. The work here to implement and optimize conditions for the use of a high efficiency single cell sample introduction system on a quadrupole ICP-MS demonstrated the establishment of a developmental platform to enable to the future development of microplastics analysis by spICP-MS. The efforts revealed that the aerosolization and filtering components of the sample introduction system, normally essential for conventional ICP-MS analyses, were critical in its effects on the transport of larger particle species. Second, the optimizations and other key parameters discovered were applied in the form of a reduced nebulizer gas flow to enable similar transport behavior of 5 μm plastic particles to 30 nm gold (Au) nanoparticles (AuNPs). Additionally, this large linear range was exploited in the establishment of SI traceable measurements using established nanoparticle standards, value assigned for particle number concentration, and through this link, the ability to resolve, accurately size, and quantify the particle number concentration of two microplastic particle species in a mixture. Finally, the optimizations and expanded linear dynamic range of spICP-MS for microplastic particles was applied to international efforts aiming to begin the process of establishing standard materials for microplastics. The analysis of a standard development material revealed that there exists unknown measurement bias when comparing measurements with clear SI traceability chains and isolated measurements without such links. The results emphasize the need for future development of even more suitable calibrations standards of microplastics and standard protocols for the further metrological advancement of the spICP-MS analysis of microplastics. The results in this work provide fundamental improvements into measurement capabilities of spICP-MS that can be further exploited by other types of microplastic samples or even other particulate samples in the same size regime of microplastics around 5 μm in size.