Monitoring compositional changes of the lipid fraction of fingermark residues deposited on paper during storage

Abstract

3Characterising the changes in fingermark composition as a function of time is of great value for 4 improving fingermark detection capabilities by understanding the processes and circumstances under 5 which target compounds become degraded. In this study, gas chromatography-mass spectrometry 6 was used to monitor relative changes in the lipids from latent fingermarks over 28 days. Principal 7 component analysis of the relative composition of 15 lipids in fingermarks showed that fingermark 8 age was a significant contributor to the variability observed in the data, but that inter-donor variability 9 was also significant. This was attributed principally to changes in the relative amounts of squalene, 10 which rapidly decreased in the fingermarks. It was also observed, however, that most fingermarks 11 exhibited relatively small changes in composition during the first seven days, followed by more rapid 12 changes up to 28 days. Significant inter-donor variation of both initial fingermark composition and the 13 rates and nature of loss processes was observed, which was reflected in the relative projection of 14 samples from different donors. Finally, samples stored with no exposure to light or airflow for 28 days 15were projected significantly closer to the samples analysed on the day of deposition than those 16 exposed to light, due to the reduced photodegradation rate of squalene. 17

Changes in latent fingermark glyceride composition as a function of sample age using UPLC-IMS-QToF-MSE

“…Light exposure has been linked to increased degradation rates of fingermark compounds such as squalene. 5,27 However, Pleik et al inferred that the accelerated ozonolysis of monounsaturated TGs in samples exposed to light might instead be due to competing degradation mechanisms and additional environmental factors such as increased exposure to air flow. 13 Similar observations were made by Hinners et al who noted that the rate of TG ozonolysis was significantly reduced when fingermarks were stored in both clear and opaque containers, compared to samples left exposed to ambient air.…”

“…The rapid oxidation of squalene, a highly unsaturated compound, has been observed in many investigations into fingermark lipid degradation. [4][5][6]16,18,27 The rate of squalene loss is accelerated by light exposure. 5,27 Cholesterol has been shown to decrease at a slower rate.…”

“…[4][5][6]16,18,27 The rate of squalene loss is accelerated by light exposure. 5,27 Cholesterol has been shown to decrease at a slower rate. 16 Further indications as to the kinds of chemical changes undergone by latent fingermark residue may be found in dermatological research, which is concerned primarily with in situ skin surface lipids.…”

Revealing the spatial distribution of chemical species within latent fingermarks using vibrational spectroscopy

“…The bulk chemical composition of fingermarks has been extensively studied, revealing that the composition of fingermarks is complex (many chemical species present), 2,8,28,29 varied (composition is influenced by the donor, 2,20,29,30 the substrate 1,31 and the environment); 3,4,15,20 and dynamic (composition changes over time). [2][3][4]32 Despite this complexity, the chemical components of fingermarks can be broadly divided into 3 categories: sebaceous material (lipophilic chemical compounds), eccrine material (hydrophilic chemical compounds), and debris such as skin cells or exogenous particles (cosmetics, dirt, etc.). Typical sebaceous, eccrine and debris components of fingermarks are presented in Tables 3 and 4.…”

Interpol review of fingermarks and other body impressions 2016–2019

“…The amount of squalene in fingermarks (obtained by GC-MS) was used as a marker of homogeneity when comparing uncontrolled and controlled deposition protocols [ 207 ]. Lipid composition and aging : The compositional changes of the lipid fraction of sebum-rich fingermarks left on paper was monitored using GC-MS [ 208 ]. By observing the relative composition of 15 lipids over 28 days, the authors confirmed previously-established trends (e.g., squalene degradation, intra- and inter-variability) and emphasized the impact of storage conditions, the dynamic of degradation, as well as the persistence of free fatty acids and wax esters over time.…”