Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry profiling of trace constituents of condom lubricants in the presence of biological fluids

Abstract

The use of condoms in sexual assault cases has become increasingly common due to the heightened awareness of the use of DNA as evidence in criminal investigations. The ability to identify and differentiate the polymers and additives found in lubricant residues can provide investigators leads and insights as to the perpetrator of a sexual assault. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) is ideal for detecting condom lubricants and additives; the instrument is capable of surveying analytes across a wide mass range and is a preferred technique for the analysis of polymers. Three MALDI-TOF-MS methods directed toward the detection and differentiation of condom and personal lubricant residues, as well as their mixtures with biological fluids, were developed and compared: (a) a sample premixed with aqueous matrix; (b) a sample premixed with an ionic liquid matrix; and (c) a layering method that incorporates a cationization reagent. Of the three, the layered method that utilized sodium chloride as a cationization reagent showed the best sensitivity and selectivity. This method allowed for the segregation of the various lubricant formulas into a discrete number of groups. Infrared spectroscopy was used to support and clarify the MALDI data. Principal component analysis was used to further demonstrate the ability of this method to segregate various lubricant types into a limited number of classes. Additionally, lubricant residues could be detected in the presence of biological fluids down to a fraction of a percent.