Forensic Discrimination of Bottle Glass by Refractive Index Measurement and Analysis of Trace Elements with ICP-MS

Abstract

Measurement of refractive index and trace element analysis by ICP-MS were applied to the forensic discrimination of bottle glass samples from different origins. Refractive index was calculated from the matching temperature at which glass fragments became invisible in the silicone oil. Sample solution for ICP-MS was prepared by dissolving approximately 10 mg of glass fragments into a mixture of 0.5 ml of HF and 0.5 ml of HClO₄ and heating for 2 h using a microwave oven, followed by dilution to 25 ml after 2 ml of HNO₃ was added. Thirteen elements (Co, Cu, Zn, Rb, Sr, Zr, Ag, Sn, Sb, Ba, La, Ce and Pb) were found to be useful for the discrimination of bottle glasses. These elements in NIST SRM 612 (Trace Elements in Glass) could be determined with an RSD less than 3.2%, except for Sn and Pb. The proposed method was applied to 16 bottle glass samples. Of 120 pairs among 16 bottle samples, 13 pairs were indistinguishable by RI only. Combination of trace element analysis by ICP-MS and refractive index measurement made it possible to distinguish all the pairs.