The rapid and accurate identification of condom-derived lubricant traces takes on heightened importance in sexual assault cases where the assailant has used a condom in order to avoid leaving behind incriminating DNA evidence. Previous reports have demonstrated that a variety of techniques can be used to confirm that a given residue is condom derived, based on the detection of spermicides, slip agents and other common additives; however, limited success has been achieved in differentiating brands from among a broad range of condom types. The current project created a database of condom residue spectra composed of 110 different condom types representing 16 brands, with the spectra serving as representative fingerprints for each brand. The spectral fingerprints were subjected to preprocessing prior to the application of Partial Least Squares Discriminant Analysis (PLS DA), which was used to generate a classifier that permitted identification of condom brands with an accuracy of 97.4 percent. An additional criterion was imposed on the PLS DA to provide the confidence level and credibility of each prediction. The effect of time since deposition, the presence of contaminants, and the influence of residue transfer on the prediction accuracy of the model were also assessed. The results from Sparse Discriminant Analysis (SDA) and PLS DA were followed by application of the Student's test to determine mz values representative of small-molecule markers that were most important for defining brand classes. The mz values revealed by the two methods were found to be consistent in indicating which masses were representative of markers. The SDA method also provided low dimensional views of the discriminative directions for classification of condom residues, thereby enabling easy visualization of the relationship between the indicated mz values and brand discrimination. The results show that the database of condom residue spectra can be used to identify residues based on differences in chemical components peculiar to each brand. The database can be readily expanded to include more condoms.
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