Optimization of extraction methodologies for condom lubricants and additives in the presence of biological fluids
Millard, Rebecca Elizabeth
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Over time, criminals have become more aware of the different types of trace evidence that are capable of being identified by forensic analysis. As a result, the frequency of actions taken to prevent the transmission of evidence, specifically biological fluids and subsequent DNA evidence, with the usage of condoms in the commission of sexual assaults, has increased. With the increased use of condoms, comes the increased awareness and probative nature of forensic analysis of the potentially unique chemical profiles residues may leave behind. This includes the identification of lubricant type and of any additives that may be present, such as spermicides, flavoring or topical anesthetics. The two predominate condom lubricants are polydimethylsiloxane (PDMS) and polyethylene glycol (PEG): PEG, a water-soluble lubricant, is soluble in polar solvents, such as methanol, while PDMS, a silicone-based lubricant, is reported to be soluble in non-polar solvents, such as hexane. A total of thirty condoms representing eight brands, each of a different type, were evaluated by Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR). It has been reported that PDMS is the more prevalent condom lubricant compared to PEG; this trend was reflected in this small subset of products. Of the thirty condom lubricants analyzed, twenty-five were PDMS (approximately 83%), six PEG (approximately 7%), six glycerol (approximately 7%) and one “other” (approximately 3%). A direct extraction method was developed to isolate the lubricant from the condoms. Following the direct extraction of the condom lubricants from ten condoms of different brands and types containing PDMS, the extraction capabilities of three solvents: hexane, methanol and methylene chloride, in the presence of blood and saliva separately, were evaluated. Two different biological fluid/lubricant sample types were created: liquid suspensions of lubricant, biological fluid and solvent; and contrived casework samples consisting of a mixture of lubricant and biological fluid dried onto a cotton swab. Hexane was capable of isolating only the PDMS lubricant in the presence of biological fluids. In an effort to extract and identify the water-soluble lubricant PEG and any additional additives, two Trojan condoms marketed as containing the spermicide nonoxynol 9 (N9) and one Durex condom marketed as containing the topical anesthetic benzocaine were obtained. Methanol was used as the direct extraction solvent as much of the published literature has determined that additives, such as spermicides and topical anesthetics, are often found in combination with PEG, which must be extracted in a polar solvent. Although capable of extracting the lubricant PEG, PDMS, and the N9 from the condoms directly, the presence of biological fluids prevented the successful isolation of any condom lubricants or additives with the use of methanol. This extraction study established the solubility of PDMS in both methanol and hexane as well as the limited solubility of PEG in methanol. To identify a solvent capable of extracting both lubricant types as well as the spermicide additive N9 in the presence of biological fluids, the extraction capabilities of methylene chloride were assessed. In the literature, methylene chloride is often used to eliminate a two-step, or two-solvent, extraction for condom lubricants. The isolation of PDMS and N9 had mixed results when using methylene chloride as a solvent. PDMS and N9 were successfully isolated and identified in one of the Trojan brand spermicidal condoms, but not the other, most likely due to a difference in concentration of N9 in the two condoms. Only PEG could be isolated in the Durex condom marketed as containing benzocaine using methylene chloride. In the blood and saliva/lubricant contrived casework samples extracted with methylene chloride, the PDMS and PEG in the respective condoms were isolated but N9 was not. An evaluation of solvent extraction efficiency was made by comparing the ability of each solvent to isolate condom lubricant and additives in the presence of biological fluids. Methylene chloride was found to be the most effective solvent when compared to hexane and methanol for this purpose.