Sample introduction systems play a crucial role in obtaining reliable analytical data. These systems are chosen and refined in accordance with the specifications of the analysis and the kind of sample that will be examined. In mass spectrometry, particularly in inductively coupled plasma mass spectrometry (ICP-MS), spray systems are used to convert liquid samples into fine droplets and introduce them into the plasma, where they are atomized and ionized. Typically, these involve nebulizers used in combination with an appropriate spray chamber. The primary function of the spray chamber is to modify the aerosol generated by the nebulizer by adjusting properties such as droplet size distribution, aerosol concentration, or particle velocity. An ideal sample introduction system should introduce only droplets with a diameter < 10 µm into the plasma and effectively separate all droplets > 10 µm. In practice, a significant proportion of useful smaller droplets is lost through contact with the walls [Fasch et al., 2022], [Fasch et al., 2023].
Understanding these processes of aerosol modification, including impact, droplet breakup or coalescence, evaporation, and turbulence effects, requires control of the flow conditions, which is difficult to access empirically. In this thesis, a computational fluid dynamics (CFD) approach is used to investigate the aerosol flow conditions produced by a micro-uptake glass concentric nebulizer in a Scott type spray chamber. Phase Doppler anemometry (PDA), laser diffraction, and particle imaging velocimetry (PIV) are used in experiments to determine the droplet size distribution produced by the nebulizer itself (primary aerosol), the droplet size distribution at the exit of the Scott spray chamber (tertiary aerosol), and velocity distributions [Fasch et al., 2022], [Fasch et al., 2023].
These data are used for the numerical calculations, both as input parameters and for validation of the CFD model. The results provide a representation of the most important transport phenomena in the chamber. The assumption that only a small fraction of the introduced sample reaches the plasma as droplets is confirmed. After varying conditions in the spray chamber, it is also verified that cooling the chamber enhances the efficiency of the sample introduction system by reducing the solvent load on the plasma. Quantitative measurements of analyte transport demonstrate that as the spray temperature increases, the mass of transported solvent increases as well, while the analyte transport efficiency stays almost constant within the investigated temperature range (2 °C to 40 °C) [Fasch et al., 2022], [Fasch et al., 2023].