Computer simulations of laser ablation sample introduction for plasma-source elemental microanalysis

Elemental microanalysis, using laser ablation for sample introduction into plasma-source spectrometry, is based on the analytical information carried by the ablated particles that are delivered to the ICP. Numerical fluid-dynamical simulations allowed us to understand the flow characteristics of the carrier gas, which influence the sample introduction and signal intensity. The carrier gas flow in the transport tubing was found to be laminar, with nested velocity paraboloids, whose front profile is less sharp for heavier carrier gases. The gas velocity is also characterized by high-frequency fluctuations along the tube length due to molecular diffusion. The temporal signal profiles were modelled considering the aerosol filling and elution rates in the setup, the whole setup dimensions, the transport efficiency, and the particle sizes, combined with a condition of mass conservation. The simulated signal intensity showed a logarithmic dependence on the transport efficiency, which exacerbates signal structure. Finally, in passing from single shot to repeated shot analysis, the transient signals were modelled calculating the convolution of the single shot profile with the laser pulse sequence profile.