Fingerprint aging from the lipid degradation: Untangling complexity in human and environmental effects

Description:
In spite of many efforts in the last few decades, there still is no reliable method to determine the time since deposition (TSD) of latent fingerprints. We have previously reported that the unsaturated fingerprint triacylglycerols (TGs) react with ambient ozone and degrade over time, and suggested it can be used to determine fingerprint age. However, there are multiple factors involved in this process, human and environmental, making it very difficult to achieve forensically useful outcome. In this work, we demonstrate our effort to untangle the complexity by mass spectrometry-based chemical analysis.

Environmental factors are studied first using a controlled environmental chamber. As expected, ozone concentration and temperature are the major factors to explain the degradation whereas humidity and light have a minimal effect. To further ensure ozonolysis is the major mechanism, fingerprints were aged in ambient condition and analyzed by high-resolution mass spectrometry for Kendrick Mass Defect plot analysis. Hundreds of fingerprint lipid peaks and their aging products were effectively analyzed through this analysis, and confirmed ambient ozonolysis is the major reaction products. Epoxidation products by singlet oxygen were also detected; however, they are in low abundance with a minimal effect by aging.

Pseudo first order kinetics model was established to derive the kinetics equation to estimate TSD. In the zeroth approximation, where all the unsaturated TGs were lump summed, a simple pseudo-first order kinetics equation was derived to calculate TSD with only two variables, ozone concentration and temperature. While this equation explains overall trend of TG degradation, it does not explain individual differences. To take this into account, subsequent refinement of the model was made to improve the kinetics, by taking the effect of the number of unsaturation in each lipid and the effect by other lipids.

Speaker: Young-Jin Lee - Iowa State University
Dr. Lee has over thirty years of expertise in mass spectrometry from fundamental gas phase ion chemistry to ion mobility instrumentation, proteomics, and mass spectrometry imaging. His current research interests include mass spectrometry imaging for untargeted spatial metabolomics and forensic fingerprint chemical analysis.