A preliminary study on the persistence of condom lubricants in the vaginal matrix

Abstract

It has been established that condom traces are evidence to consider in sexual assaults and rape cases, but gaps in the interpretation of the evidence have been highlighted. Condom lubricants, more specifically silicone lubricants, are known to transfer in the vaginal matrix and can be easily recovered when analysed with infrared spectroscopy. The interpretation of condom evidence in forensic science requires a better understanding of mechanisms such as background, transfer, and persistence of the traces in a given matrix.This work aimed to use Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS-FTIR) to provide an empirical dataset addressing the persistence of transferred silicone lubricants in the vaginal matrix. Swabs for condom traces were self-collected from volunteers at different post-coital intervals ranging up to 36 h post-coitus. The effect of the time elapsed between the intercourse and the time of sample collection was investigated, and a preliminary observation of the activity of the claimant as an influence factor is also discussed.Silicones were easily detected up to 18 h post-coitus, while the vaginal matrix dominated the spectra after 36 h. At 24 h post-coitus, the results were not reproducible, which makes it difficult to assess a persistence at this time. The data were found to vary between the participants, but a similar trend was observed in the exponential decay. Finally, the activity of the volunteer was found to be one of the key parameters to the loss and differences in absorbance which were observed in the data. It was observed that when volunteers were taking a shower, which is likely to happen with real world cases, silicone persistence was also affected.