Novel Ambient Oxidation Trends in Fingerprint Aging Discovered by Kendrick Mass Defect Analysis

A Kendrick mass defect
(KMD) plot is an efficient way
to disperse
complex high-resolution mass spectral data in a visually informative
two-dimensional format which allows for the rapid assignment of compound
classes that differ by heteroatom content and/or unsaturation. Fingerprint
lipid oxidation has the potential to be used to estimate the time
since deposition of a fingerprint, but the mass spectra become extremely
complex as the lipids degrade. We apply KMD plot analysis for the
first time to sebaceous fingerprints aged for 0–7 days to characterize
lipid degradation processes analyzed by MALDI-MS. In addition to the
ambient ozonolysis of fingerprint lipids previously reported, we observed
unique spectral features associated with epoxides and medium chain
fatty acid degradation products that are correlated with fingerprint
age. We propose an ambient epoxidation mechanism via a peroxyl radical
intermediate and the prevalence of omega-10 fatty acyl chains in fingerprint
lipids to explain the features observed by the KMD plot analysis.
Our hypotheses are supported by an aging experiment performed in a
sparse ozone condition and on-surface Paternò–Büchi
reaction. A comprehensive understanding of fingerprint degradation
processes, afforded by the KMD plots, provides crucial insights for
considering which ions to monitor and which to avoid, when creating
a robust model for time since deposition of fingerprints.