Comparison of spectroscopic methods in the detection of silicone-based condom lubricant evidence

Abstract

Spectroscopic techniques, such as infrared and Raman spectroscopy, are very powerful and valuable tools for analysing evidence in forensic sciences. In sexual assault cases, vibrational spectroscopy has been reported as a useful screening method to detect condom residues. However, there has been no study to identify which specific method could be the most suitable technique for the analysis of silicon-based lubricants as forensic evidence. This study looked at the different reported infrared and Raman techniques. The aim was to develop an adequate spectroscopic technique for polydimethylsiloxane (PDMS) analysis and detection. Five FTIR sampling techniques were assessed: ATR, micro-ATR, DRIFTS, transmission and micro-transmission. Raman spectroscopy was assessed with four lasers and included imaging/mapping techniques. The techniques were evaluated on the basis of sensitivity, analysis time, and sample preparation method and time. Although ATR techniques offer good reproducibility, the spectral quality was lower than that obtained with transmission and DRIFTS techniques. Raman spectra were found to be less informative and of lower quality than infrared spectra. Considering case work sample analysis, where material from swabs will need to be extracted, DRIFTS was found to be the best method for trace evidence analysis, although the sample preparation time is longer than for ATR.