A model for the generation of small particles in laser ablation ICP-MS

A model for generation of small particles from laser ablation products under a helium or argon atmosphere is proposed. The conditions employed in the model correspond to a typical LA-ICP-MS measurement. It is shown that small particles with a size up to 100 nm can be produced by gas-to-particle conversion with a subsequent coarsening due to particle coalescence. The two mechanisms can be separated in a physical meaningful way and modeled independently. The particle distribution function is calculated for different background gases. The calculations demonstrate that the small particle fraction of the total particle distribution is not significantly influenced by a change of background gases. It is shown how these particles contribute to the total particle distribution. The discussion illuminates under which conditions small particles, which have been found favorable for the analytical performance of an ICP, are predominantly produced. Qualitatively, the mechanism allows understanding the size dependent chemical composition of the particles. The calculations are compared with preliminary brass ablation experiments and good agreement is found.