| Inductively coupled plasma mass spectrometry (ICP-MS) is becoming a widely used method for elemental analyses of glass fragments, with laser ablation (LA) of solid samples being the most efficient introduction system for forensic applications (e.g. Trejos et al., 2003). Trace element abundances in glasses are widely variable, even in glasses of the same refractive index. This variability allows for a high degree of discrimination when comparing ratios of trace element abundances. Laser ablation requires little or no sample preparation, which reduces opportunity for contamination, and is virtually non-destructive. In order to use the technique for routine forensic analyses of glass fragments in casework, it was necessary to test the precision of the technique and the homogeneity of samples to avoid erroneous interpretations of the results. A protocol for the analysis of glass fragments by LA-ICP-MS was developed using a set of ten "unknown" automobile float glass fragments and a National Institute of Standards and Technology glass. A graphical technique was employed for comparing element ratios in samples, based on the work of Watling et al. (1997). After confirming the homogeneity of glass samples and ensuring reproducibility of individual analyses, the technique was applied to casework for the Michigan State Police. When samples cannot be distinguished by physical parameters such as refractive index, they are analyzed by LA-ICP-MS. Three cases are presented as examples of the discriminatory and associative power of the method. |
