Characterization and comparison of tape evidence using elemental profiling methods and chemometric analyses

As submitted by the proposer: This research aims to evaluate and validate the scientific reliability of elemental profiling methods for the forensic examination of tapes using SEM-EDS, uXRF, LIBS and LAICP-MS. Tape examiners rely on physical and chemical characterization to support the evidential value of tape evidence comparisons. Previous studies have shown the utility of elemental analysis for the chemical characterization of tapes including the use of SEMEDS or u-XRF. These techniques, however, have some limitations regarding their selectivity and sensitivity and very few studies report their analytical performance in tape examinations. The proposed effort evaluates conventional SEM-EDS and u-XRF methods and incorporates the use of LIBS and LA-ICP-MS to offer improved discrimination among different tape sources, leading to interpretations that will improve the value of tape evidence associations. The advantages of laser ablation methods (LAICP-MS and LIBS) make these tools attractive for forensic analysis due to their speed of analysis, high discrimination capabilities and their remarkable sensitivity, precision and selectivity. More than 30 forensic laboratories around the world, most of these in the US, are currently using laser ablation methods and many more are expected to adopt these
technologies since cost-effective instruments are now commercially available and the number of meaningful applications are being adopted. Tapes used in various crimes are one type of evidence that could benefit from the use of these methods but the application of LIBS and LA-ICP-MS to tape evidence analysis has remained unexplored to date. The proposed 2-year research aims to provide a comprehensive study to validate elemental analysis methods for tape examinations by evaluating the validity of the methods in terms of their analytical performance, discrimination potential, informing power, uncertainty and error rates. A collection set of over 250 tapes (duct and electrical) will be used to study inter-roll and intra-roll variations and its relation to tape manufacturing and distribution in order to make informed decisions about sampling, chemical analysis and interpretation of the data collected. Experienced trace examiners and statisticians will collaborate with our research group to incorporate statistical tools that are suitable to the particular sensitivity and precision level of the proposed methods as well as for crossvalidation studies. This project will make an important contribution by strengthening the scientific foundation for interpretation of elemental analysis by conventional methods and by further developing highly discriminating LIBS and LA-ICP-MS methods for tape examinations. The dissemination strategies will include peer reviewed publications, presentations and online discussion forums.

This project contains a research and/or development component, as defined in applicable law.

ca/ncf