Characterization of laser ablation sample introduction plasma plumes in fs-LA-ICP-MS
Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a well-established elemental analysis technique which has been applied to a variety of fields. However, LA-ICP-MS still faces substantial challenges in the deviation of detected elemental concentrations from the known composition of the sample, or elemental fractionation. Applying optical emission spectroscopy (OES) during the LA process for LA-ICP-MS can help to characterize the emitted plasma plume and potentially identify sources of elemental fractionation during LA. We characterize LA sample introduction plume using OES during fs-LA-ICP-MS analysis of a brass sample. Fundamental plume parameters, i.e., electron temperature and density are estimated and correlated with ICP-MS signal characteristics, which give insight into how laser ablation plume parameters are related to LA-ICP-MS results. The hydrodynamic expansion features of fs-LA sample introduction plumes are evaluated using shadowgraphy and time- and spectrally-resolved fast-gated photography. Results showed dissimilarities in Cu I and Zn I expansion features. There is a very good correlation between the ICP-MS signal intensities and characteristic parameters of the sample introduction plumes. However, the crater formation during single spot ablation caused significant changes in line emission intensities though the estimated temperature and density showed constant values.