The Analysis of the Fatty Acid Content of Fingerprint Residues Using Gas ChromatographyMass Spectrometry

Abstract

The Analysis of the Fatty Acid Content of Fingerprint Residues Using Gas Chromatography/Mass Spectrometry Ashley CochranOne of the recurring issues in the practice of forensic science is human subjectivity, especially within the field of fingerprint examination. Smudged fingerprints at crime scenes that contain little to no ridge detail often cause problems for examiners who, in turn, are unable to make identifications or exclusions in the absence of DNA markers. In recent years, researchers have explored the chemical composition of fingerprint residues to either provide an alternative means for including or excluding potential donors, or to provide investigative leads. Research into the chemical composition of fingerprints has shown that it may be possible to determine sex, age, and race from residues that are left behind when a fingerprint is deposited on a surface. However, it is important to first ensure that residues deposited by one individual remain consistent over a period of time.In this study, five different types of skin residues (natural, eccrine, face, neck, and groomed fingerprints) were collected from six participants over the course of 56 days to assess both intra-and inter-subject variability of the different sample types. Natural prints consisted of any substances that were on the participant's hands upon arrival at each collection event. Eccrine residues were collected after washing hands with soap and water. Groomed prints were collected after rubbing hands across the subject's own face and neck. The measured variables were the relative quantities of fatty acid methyl esters (FAMEs), squalene, and cholesterol in each subject's residues. The fatty acid methyl esters were analyzed using a conventional gas chromatography/mass spectrometry (GC/MS) instrument. Canonical discriminant analysis (CDA) was used to classify the data into known grouping factors to determine if there were sufficient differences between the residues of different samples or subjects to enable classification between groups.The results show that within an individual, 82% of the original grouped cases were correctly classified and 62% of the cross-validated grouped cases were correctly classified to the correct source of the sample. In other words, there are significant chemical differences between the five types of samples collected from an individual. Natural and eccrine residues generally contained the fewest compounds and in the lowest amounts and were not helpful for discriminating between individuals. Saturated fatty acids such as C16:0 and C18:0 were the most commonly observed compounds in the natural and eccrine residues. Groomed fingerprint residues contained more FAMEs than the natural and eccrine residues, although not as many FAMEs as the face and neck residues. Using leave-one-out cross validation, classifying subjects using a fixed sample type, like face or neck, provided better than 92% and 77% accuracy, respectively, even when including the intra-subject variability over a 56-day period. The results indicate tha...