Evaluation of Uncertainty in Commonly used Techniques

Crime laboratories have many instruments and associated methods that they utilize to analyze trace evidence. Some of the most commonly used include light and other microscopies, Fourier transform infrared spectroscopy (FTIR), and microspectrophotometry (MPS). The STG has been working with trace evidence examiners to understand their practices, and find areas where potential improvements could be made. One area we have focused on is the use of diamond compression cells for transmitted light FTIR. Understanding how the compression cell is used and how pressure from different examiners might affect measurements could be a way to reduce variability. Work is being undertaken to use an adapter to standardized the pressure applied with the compression cell, and observe its effects on the resulting transmission FTIR spectra. These spectra are being analyzed with the help of the Statistical Engineering Division (SED) to look at the variability produced by different pressures in the compression cell. Work in areas like this will continue to evaluate techniques forensic examiners already have available to them in their labs, so that we can aid them in improving the reproducibility and reliability of their analyses.