The development of objective approach to the characterization and interpretation of paint evidence by SEM/EDS

Elemental analysis by energy dispersive x-ray spectrometry (EDS) in a scanning electron microscope (SEM) represents a critical component of forensic paint comparisons, which is among the most common analyses performed by trace evidence laboratories. Currently, the elemental analysis of paint by SEM/EDS is well-utilized method by most laboratories conducting forensic paint comparisons.

The approach is currently defined as an ASTM E2809 guide, with the following issues: a) the analytical approach is only loosely constrained with little research and support provided for the selection of key sample preparation methods and analytical parameters; b) the current approach has been criticized by the microanalysis community and the scientific impact of the issues raised are presently unknown due to a lack of foundational research; and c) interpretation of data derived from this guide is presently based upon a subjective evaluation of analytical results.

By taking advantage of advances in SEM/EDS hardware and software, coupled with a carefully selected sample set, these issues can be resolved and used to improve the current best practices by providing tighter constraints on sample preparation approaches, analytical conditions, and, most importantly, developing interpretation methods based upon an objective, reproducible process.

This research is proposed in direct response to shortcomings of the current ASTM guide to the elemental analysis of paint, and all aspects of this research are aimed at providing practical and readily applicable improvements to the current best practices. It is anticipated that the outcome of this research will provide: a) an empirical and theoretical basis for the selection of analytical approach and analytical variables; and b) the first practical quantitative approach elemental comparison of paint samples by SEM/EDS with the potential for increased analytical discrimination by utilizing not only the average elemental composition of the sample but also the shape, size distribution, and composition of fillers and pigment inclusions that are present but currently overlooked in the existing best practice.

The research will present results in a manner that permits a direct comparison to existing best practices, which to date, have not themselves been sufficiently evaluated to determine their own efficacy.

This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

ca/ncf