This study evaluates the capability of μ-XRF and LIBS analyses to characterize the homogeneity (elemental variation) of glass compared to the LA-ICP-MS quantitative analysis method.
Two premises in the forensic comparison of glass are that 1) the elemental composition across a single source (e.g., a pane) is homogeneous and 2) the elemental variation within a single source is much smaller than the elemental variation observed among different glass sources (different panes manufactured at different sites or different times). These assumptions are widely supported when using microsampling methods such as LA-ICP-MS; however, systematic homogeneity studies using μ-XRF and LIBS methods are unavailable. In this study, the variability of the elemental composition within 100 fragments from two different panes of the same windshield was characterized using chemical maps, and semi-quantitative data was used to compare fragments within and between the different panes. When comparing pieces within the same pane, the variability for most elements was less than 10% RSD for both μ-XRF and LIBS and less than 5% RSD for LA-ICP-MS. Comparison methods simulating casework situations in which one questioned fragment is compared to more than one known fragment resulted in better performance as the number of fragments of the known sample increased (to up to 4 fragments, 12–20 measurements). The results show the comparison criteria should be selected according to the instrument’s precision and sensitivity. Error rates below 3% were obtained for μ-XRF and LIBS when selecting the appropriate number of fragments, measurements, and comparison criterion. (Publisher Abstract)