Forensic discrimination of sheet glass exposed to high temperature by the determination of trace impurities using ICP-MS

The effect of heating on the refractive index (RI) and trace elemental compositions of glass was investigated in order to develop an accurate discrimination method of glass fragments exposed to the high temperature of fire on illegal entrance into a crime scene for robbery. Fragments taken from 5 different sheet glasses were subjected to RI measurement and analysis of trace elements using ICP-MS before and after heating at 764 degrees C for 2 min. The difference in the RI between the heated and non-heated fragments ranged from 0.0012 to 0.0015, which corresponds to 6 times more than the variation of the RI within a pane of glass. In contrast, profiles of 10 elements (Co, Rb, Sr, Zr, Mo, Ba, La, Ce, Nd and Pb) in glass exhibited no significant difference between the heated and non-heated ones. In conclusion, the forensic discrimination of glass fragments must be performed not by RI measurement, but by analysis of the elemental compositions when glass evidence could be exposed to the high temperature of fire.