Campbell Gareth P, Gordon Amanda L
The Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
J Forensic Sci. 2007 May;52(3):630-42. doi: 10.1111/j.1556-4029.2007.00411.x.
The detection of DNA is inhibited in cases of sexual assault involving condom use. Trace evidence, including condom lubricant residues, provides crucial associative evidence in such cases. The existing Fourier transform infrared spectroscopy (FTIR) methods for lubricant analysis and detection are limited with regard to sensitivity and discrimination. The aim of this research was to establish a new method as an alternative to FTIR for the analysis of condom lubricant residues. Pyrolysis gas chromatography-mass spectrometry (PyGC-MS) and GC-MS are highly sensitive methods of analysis for a wide range of chemical substances. PyGC-MS and GC-MS were used to analyze condom lubricants in standard solution, from clean swabs and from postcoital swabs. Pyrolysis of polydimethylsiloxane (PDMS) lubricant forms cyclic products known as cyclic dimethyl siloxanes (DMS), which are separated and detected by the GC-MS. The polyethylene glycol (PEG) lubricant can be analyzed by GC-MS directly from solution. The methods of extraction and analysis presented in this paper were shown to be significantly more sensitive than FTIR for the analysis of PDMS and PEG condom lubricants. PDMS was detected as low as 1 mug in standard solution and from clean swabs using the PyGC-MS method. PEG was detected as low as 0.5 microg from standard solution and 50 mug from clean swabs using the GC-MS method. Unfortunately, we were unable to provide further discrimination between condom brands and subbrands. The methods established throughout the research were used successfully to detect condom lubricants from donated postcoital swabs. Lubricants were detected in abundance on swabs 12 h postcoitus. Recommendations are made regarding implementation of new methods for routine analysis of casework samples along with strict pyrolysis interpretation criteria to minimize the possibility of misinterpretation of false positives.
在涉及使用避孕套的性侵犯案件中，DNA检测会受到抑制。微量证据，包括避孕套润滑剂残留，在此类案件中提供了关键的关联证据。现有的用于润滑剂分析和检测的傅里叶变换红外光谱（FTIR）方法在灵敏度和鉴别能力方面存在局限性。本研究的目的是建立一种新方法，作为FTIR的替代方法用于分析避孕套润滑剂残留。热解气相色谱-质谱联用（PyGC-MS）和气相色谱-质谱联用（GC-MS）是对多种化学物质进行高灵敏度分析的方法。PyGC-MS和GC-MS被用于分析标准溶液、干净拭子以及性交后拭子中的避孕套润滑剂。聚二甲基硅氧烷（PDMS）润滑剂热解会形成环状产物，即环状二甲基硅氧烷（DMS），它们可通过GC-MS进行分离和检测。聚乙二醇（PEG）润滑剂可直接从溶液中通过GC-MS进行分析。本文所提出的提取和分析方法在分析PDMS和PEG避孕套润滑剂时，显示出比FTIR明显更高的灵敏度。使用PyGC-MS方法，在标准溶液和干净拭子中，PDMS的检测下限低至1微克。使用GC-MS方法，在标准溶液中PEG的检测下限低至0.5微克，在干净拭子中低至50微克。遗憾的是，我们无法进一步区分不同品牌和子品牌的避孕套。在整个研究过程中建立的方法成功用于检测捐赠的性交后拭子中的避孕套润滑剂。在性交后12小时的拭子上大量检测到了润滑剂。针对将新方法用于案件样本常规分析的实施提出了建议，并制定了严格的热解解释标准，以尽量减少误判假阳性结果的可能性。
