Predicting Fingerprint Age Based on Ozonolysis Kinetics of Unsaturated Triacylglycerol Degradation

Answering the question, "How old is a fingerprint?", is a highly sought-after aim in forensic science. Despite several decades of studies to find an empirical correlation in fingerprint aging, there has been no reliable method so far. In this study, we attempt to determine the time since deposition (TSD) of aged fingerprints from the chemical profile captured within a matrix-assisted laser desorption/ionization mass spectrometry data set. Our approach is based on the chemical kinetics associated with the ambient ozonolysis of unsaturated triacylglycerols (TGs), a major component in fingerprint lipids. First, ozone concentration and ambient temperature were determined to be the major factors in the degradation of unsaturated TGs. A simple kinetics model is then developed to describe the decay of unsaturated TGs, dictated only by the temperature and ozone concentration. This model is then applied to the degradation of TGs in a mixture of TG standards and multiple individuals' fingerprints. The overall decay of unsaturated TGs follows the pseudo-first-order reaction kinetics, validating our hypothesis; however, there are significant person-to-person variations in the initial abundance of unsaturated TGs and the decay rate, hampering the accurate prediction of TSD unless they are corrected for each individual. Nevertheless, the model's applicability for ambient fingerprint aging data was successfully demonstrated.