A critical assessment of laser ablation ICP-MS as an analytical tool for depth analysis in silica-based glass samples

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a versatile technique for trace element analysis with respect to depth in s olid samples. The high sensitivity of ICP-MS makes it possible to determine most elements in the periodic table at trace levels (< 1 mu g g(-1)). Rece nt trends in the development of instrumentation have led to the possibility of analysing craters of smaller diameter with variable depth. However, a m ajor limitation to this approach for depth profiling, preventing accurate a nd precise analysis, is element-selective, non-reproducible ablation. The a bility for representative sampling during depth analysis is tested in this study by ablating into homogeneous silica-based glass materials. Elemental relative response deviations of up to 300% are observed for selected elemen ts during progressive ablation into the glass target. The geometry of the a blation crater controls the accuracy of sampling of the material at depth. Elemental fractionation becomes significant for some elements (e.g., Zn, Pb ) when the depth/diameter ratio of the ablation crater is > 6, correspondin g to a 50% reduction in analyte response. Large diameter craters, if ablate d with sufficient laser power density, reduce elemental fractionation and g ive a larger signal for a longer period of time, providing more suitable co nditions for representative analysis. LA-ICP-MS can be a powerful technique for depth profiling provided that optimum analytical conditions are select ed.