Forensic Identification of Condom Lubricants by Advanced Statistical Analysis Processing of Direct Analysis in Real Time Mass Spectrometric Data – Towards Development of a Condom Residue Database for Forensic Science Practitioners
Date of Award
Bachelor of Science
Rabi A. Musah
The ability to identify condom derived trace evidence is gaining importance because of the increasing frequency with which perpetrators of sexual assault use condoms in order to avoid leaving behind incriminating DNA evidence that might link them to the crime. Although DNA remains the gold standard for sexual assault evidence, other forms of trace evidence are needed in its absence. When condoms are used, the lubricants associated with them are the trace evidence. For the lubricant residue to be useful in a forensics context, a database of chemical signatures of lubricants against which acquired evidence can be screened is required, so that condom brands and types can be identified from the trace evidence. Towards the goal of developing such a database, this study used direct analysis in real time-high resolution mass spectrometry (DART-HRMS) to analyze 110 different types of condoms representing 16 brands. Over 700 spectra were acquired, each serving as a chemical fingerprint for the analyzed condom. The results showed that condoms of the same type within different brands exhibited the same chemical signatures, which differed from condoms of other brands, even when the condoms were advertised to have the same characteristics. For example, the mint flavored condoms of different brands had distinct diagnostic chemical signatures that allowed them to be distinguished from one another, even though they all contained the same chemical components that conferred the mint flavor. Both supervised and unsupervised multivariate statistical analyses were performed on the data. Hierarchical clustering analysis (unsupervised) showed that condoms could be differentiated by brand. Kernel discriminant analysis (supervised) showed that condoms within a given brand could be distinguished. The observed leave-one-out cross validation was 90-100% depending upon the brand. This indicates that a strong database has been developed with the capability of serving as a presumptive test that can be used not only to identify brands, but also the particular condom type within a brand. This database can be readily expanded as additional condom types emerge, and may be particularly useful for corroborating the accounts of victims, or exonerating the falsely accused in cases where DNA evidence is lacking. The positive brand identification of unknown condom residues implies that the database could serve as a tool to assist forensic science practitioners in prosecuting sexual assault cases.
Coon, Allix M., "Forensic Identification of Condom Lubricants by Advanced Statistical Analysis Processing of Direct Analysis in Real Time Mass Spectrometric Data – Towards Development of a Condom Residue Database for Forensic Science Practitioners" (2018). Chemistry. 10.