Femtosecond laser ablation inductively coupled plasma mass spectrometry: Transport efficiencies of aerosols released under argon atmosphere and the importance of the focus position

Although the utilization of helium as aerosol carrier has been shown to improve both accuracy and sensitivity of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), occasionally, argon is being used due to practical and economic reasons. In order to provide more insight into the mechanisms underlying these performance differences, in this study, transport efficiencies of aerosols released by NIR- and UV-femtosecond laser ablation (LA) of brass applying laminar or turbulent in-cell flow conditions and argon as carrier gas were measured. Aerosol particles were collected by low-pressure impaction or filtered by fine porous membranes. On the basis of aerosol masses collected and mass differences derived from target weighing prior to and after LA, transport efficiencies approximately varied in between 75% and 95%. In addition, LA of a thin Cr layer was performed which allowed to release a well-defined amount of material and, thus, to correct mass balances for debris accumulating around the crater rim. The total aerosol mass released during LA was found to be strongly dependent on the relative focus position, i.e. surface area irradiated, even if the laser pulse energy delivered to the target was kept constant. Furthermore, a physical model only making use of input parameters such as laser spot size and pulse energy was implemented to qualitatively describe the correlation between aerosol mass and laser focus position.