Analysis of nanoparticle composition using laser ablation inductively coupled plasma quadrupole mass spectrometry

Abstract

Due to their unique properties, nanoparticles (NPs) play a critical role in various fields such as catalysis, materials manufacturing and medicine. Therefore, the need for accurate characterization of NPs is high for manufacturing processes as well as for assessing the impact on the environment and human health. Single particle (SP) inductively coupled plasma (ICP) mass spectrometry (MS) has become a valuable analytical tool for sensitive investigation of NP composition. The ion signal durations of NPs produced in the ICP are in the order of a few hundred microseconds, which allows the analysis of a single element per NP using modern ICP-MS instruments. However, due to the sequential measuring principle of quadrupole mass analyzers, a settling time between m/z values of interest is required, therefore prolonging the needed time for the acquisition of one data point. This prevents conventional mass analyzers from dual-elemental analysis of NPs. However, using modern triple quadrupole MS instruments, collision / reaction gases can be used to stretch the signals and detect them using short analysis cycles. In this thesis, laser ablation ICP-qMS was employed to analyze gadolinium-doped ceria (GDC) NPs, focusing on extending the transient ion signal duration to enable dual-element detection within single particle events. By introducing oxygen as collision/reaction gas in a triple quadrupole setup, the duration of ion cloud signals of cerium and gadolinium were prolonged roughly by a factor of 10. In combination with short measuring times per data point, this peak broadening effect allowed acquisition of multiple data points per particle event for both elements, significantly improving the reliability of compositional analysis. Quantitative calibration was performed using polyvinyl pyrrolidone (PVP) thin films spiked with defined amounts of elemental standards, eliminating the need for reference NP materials. This approach enabled simultaneous determination of NP composition and size distribution.