Ambient-air ozonolysis of triglycerides in aged fingerprint residues

Abstract

In forensic science, reconstructing the timing of events occurring during a criminal offense is of great importance. In some cases, the time when particular evidence was left on a crime scene is a critical matter. The ability to estimate the fingerprint age would raise the evidentiary value of fingerprints tremendously. For this purpose the most promising approach is the analysis of changes in the chemical compositions of fingerprint residues in the course of aging. The focus of our study is the identification of human specific compounds in fingerprint residues, characterized by a significant aging behavior that could analytically be used for the age determination of fingerprints in future. The first challenge is the sensitive detection of trace amounts of relevant human specific fingerprint compounds. Highly sensitive LC-MS methods were developed for the reliable structure identification of unsaturated triglycerides and their natural degradation products in order to proof the aging mechanism that takes place in fingerprint residues. Thus our results build the fundamental basis for further forensic method development and potential application in forensic investigation. Ozonolysis was found to be one of the major lipid degradation pathways in fingerprint residues in ambient air. High-resolution tandem mass spectrometry (HRMS) was carried out to identify the ozonolysis products (TG48:0-monoozonide) formed under exposure to the highly reactive ozone in atmospheric air. The obtained products were confirmed by matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). Despite several challenges and limitations in the age estimation of fingerprints, the identification of individual degradation products of specific unsaturated lipids in aged fingerprint samples represents a significant analytical progress, resulting in a strong increase in the validity of chemical analysis of fingerprints.

An untargeted lipidomic approach for qualitative determination of latent fingermark glycerides using UPLC-IMS-QToF-MSE

“…These compounds are predominantly unsaturated, and so may therefore be useful targets in the monitoring of chemical changes in fingermark residue over time. 29 As a comparison, 27 TG families have been previously identified in latent fingermarks, with possible structures assigned to all but 2, 10 and 94 families and 142 species separately in human sebum. 27,49 Major observed neutral losses for all glycerides for the most part corresponded predominantly to the free fatty acid species previously reported in the literature.…”

“…[24][25][26] The total profile of the constituent fatty acids exhibits similar high variability. 19,27,28 In the weeks following fingermark deposition, TGs may be prone to degradation to free fatty acids, 4 ozonides, 29 and eventually shorter chain organic compounds 30,31 , depending on environmental conditions. Such processes contribute to the changes in chemical and physical properties of the latent residue which can affect detectability, and may provide a basis for the estimation of the age of a latent fingermark.…”

“…Such processes contribute to the changes in chemical and physical properties of the latent residue which can affect detectability, and may provide a basis for the estimation of the age of a latent fingermark. 17,29 The exact glyceride species present in human sebum or latent fingermarks remain relatively underinvestigated in comparison to the smaller, more volatile sebaceous compounds which are amenable to gas chromatography (GC) separation. 1,4,18,[32][33][34] Despite this, TGs in particular are considered an important class in fingermark residue, as their presence provides a target for lipid-sensitive detection methods such as lipophilic dyes, [35][36][37] and may assist in the successful application of metal deposition techniques such as physical developer and single metal deposition.…”

“…32 Most recently, Pleik et al examined the degradation process of unsaturated TGs by ozonolysis, focusing on a single TG. 29 As described above, the fatty acid profile of sebaceous triglycerides has been researched extensively in the field of dermatology, but limited data is available in the literature regarding intact glycerides, due to their complexity. 49,50 Michael-Jubeli et al utilised high-temperature GC to separate skin surface lipids following trimethylsilylation, which enabled the characterisation of 5 monoglycerides (MGs), 7 families of DGs and 35 families of TGs.…”

“…In the context of latent fingermark analysis, it has thus far seen very limited use, with focus constrained only to a narrow range of targeted compounds. 16,29,55 Conversely, numerous methods have been developed for lipidomics analyses targeting TGs in a variety of biological samples, 52 including plasma and tissues, 56,57 animal fats 41,58 and vegetable oils. 25,40,42,58,59 Camera et al reported a high performance liquid chromatography (HPLC)-MS method to simultaneously analyse all classes comprising the 'sebum lipidome', including over 100 glycerides, demonstrating the potential of such an approach to be applied to latent fingermarks.…”