Forensic elemental analysis of materials by laser induced breakdown spectroscopy (LIBS)

Abstract

Materials analysis and characterization can provide important information as evidence in legal proceedings. Although the utility of trace elemental analyses for comparisons of glass, paint chips, bullet lead and metal fragments has been shown to offer a high degree of discrimination between different sources of these materials, the instrumentation required for the generation of good analytical data in forensic comparisons can be beyond the reach of many forensic laboratories. Scanning Electron Microscopy with an Energy Dispersive Spectrometer (SEM-EDS), X-Ray Fluorescence (XRF), Laser Ablation Inductively Coupled Plasma Atomic Emission Spectroscopy (LA-ICP-AES) and, more recently, LA-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) have been used in forensic laboratories for elemental analysis determinations. A newly developed Laser Induced Breakdown Spectroscopy (LIBS) instrument (Foster and Freeman Ltd., Evesham, U.K.) has been evaluated as a tool for the forensic elemental analysis of glass and compared in performance to other elemental methods in order to determine the utility of comparing casework sized glass samples. Developments in the instrumental design of this LIBS system, which is specifically designed to address the analytical requirements of the forensic laboratory, are presented. The utility of the LIBS system for the analysis of glass, paint, metals, gun shot residue and other matrices are also presented. The power of the LIBS-based elemental analysis to discriminate between different glass samples is also compared to the discrimination power of SEM-EDS, XRF and LA-ICP-MS. The relatively low cost (expected to be ~ $ 60,000.), ease of operation and almost non-destructive nature of the LIBS analysis makes the technique a viable forensic elemental analysis tool.