Investigation of Water-Soluble Lubricant Components for Sexual Assault Casework

Abstract

There is an increased usage of condoms in sexual assault cases to reduce the likelihood of transferring biological evidence from the suspect to their victim. Sexual lubricants may be crucial evidence in sexual assault investigations, which can act as an additional link between the suspect and the victim and/or crime scene in cases where biological evidence is not available. There are three types of condom lubricants: silicone-based, oil-based, and watersoluble. Abundant research has been carried out on silicone-based lubricants due to its commonness on the condom market. Water-soluble lubricants have been researched to a lesser extent. This thesis will focus on increasing the knowledge on the persistence of water-soluble condom or personal lubricant components by using Gas Chromatography – Mass Spectrometry (GC-MS). The water-soluble components investigated included polyethylene glycol, propylene glycol, and glycerol, and a topical anaesthetic called benzocaine. This research was split into three aims, which were to investigate the transfer and/or persistence of water-soluble lubricant components (1) on pre-loaded and controlled swabs after different extraction methods, (2) on swab remains and the supernatant after DNA extraction of controlled swabs, and (3) in the vaginal cavity and on the penis after sexual intercourse. On top of the three aims, analytical instrumental and method validation was carried out on the non-polar column and polar column of the GC-MS by determining the limit of detection of the analytes of interest. The results showed that the polar column is the best for propylene glycol, glycerol, and benzocaine. Polyethylene glycol showed poor resolution and separation on the polar column. This study also briefly looked into double-shot pyrolysis GC-MS to determine if a single-extraction method for silicone-based and water-soluble lubricants was possible. The methods developed only allowed for the detection of glycerol. Results showed that using hexane prior to the methanol extraction for water-soluble lubricant components would result in the loss of said components by at least 10% to 25%. Reversing the method by carrying out the methanol extraction before the hexane wash for the extraction of silicone-based condom components would result in the loss of 34.6% of said component. Polyethylene glycol was not detected on the swab remains after DNA (deoxyribonucleic acid) extraction, nor in the supernatant at detectable levels. Approximately 1% of propylene glycol, 5% of glycerol and 1% of benzocaine were transferred to the methanol extract of the supernatant. The presence of glycerol on the swabs routinely used for evidential swabs has resulted in a higher percent recovery of glycerol. Only benzocaine was detected on the postextraction swab remains, with the percent recovery of 5% to 13%. The persistence study determined that propylene glycol and glycerol can persist in the vaginal cavity for up to six hours, and on the penis for up to 10 hours post-intercourse. Unfortunately, the lack of participants has made it difficult to create a more accurate model of the persistence rate of condom lubricants in both biological matrices of interest. The results of this thesis lead to recommendations for routine analysis of casework samples for water-soluble lubricant components.