Ageing of Fingermarks: Monitoring the Effect of Ozone Exposure on the Composition of Fingermarks using MALDI-FT-ICR-MS

Abstract

Fingermarks have been used as physical evidence since the late 1800s, due to their highly individualistic properties. Fingermark residue also contains chemical information which may pertain to the characteristics of the donor and also the time since deposition of the fingermark. As of yet, there is no published method for the age determination of fingermarks. The aim of this thesis was to characterise the changes chemical composition of a fresh fingermark as it aged with exposure to atmospheric ozone. MALDI-FT-ICR-MS (matrix-assisted laser desorption ionisation-Fourier transform-ion cyclotron resonance mass spectrometry) was used to analyse fresh fingermarks and fingermarks that had been exposed to ambient ozone for set time frames, and their major constituents were determined. Initial method development tested two different MALDI matrices to determine the most appropriate MALDI matrix for the analysis of fingermarks, as well as determining the ideal MALDI matrix to sample ratio. Two triacylglycerols and an oleic acid standard, as well as a sample of Extra Virgin olive oil, were analysed using MALDI-MS to determine adduct formation and ozonolysis products. A clear difference between the composition of a fresh fingermark and an ozone exposed fingermark was observed. Triacylglycerols and unsaturated fatty acids were present in high signal intensities in the fresh fingermark residue, while aged fingermarks contained more diglycerophosphates and saturated fatty acids. Other compounds, such as cholesterol, dicarboxylic acids, and an eicosanoid were also tentatively identified as constituents of aged fingermark residue. Unsaturated fatty acids present in fingermark residue would suggest that the fingermark is less than 1.5 weeks old, while a high intensity signal for saturated fatty acids would suggest that the fingermark is at least 12 weeks old. Similarly, a high intensity for dicarboxylic acids and the presence of tricarboxylic acids suggests that the fingermark is at least 12 weeks old. The presence of oxoacids within the fingermark may be indicative of a fingermark that is approximately seven weeks old, as oxoacids are the intermediate product between unsaturated fatty acids and dicarboxylic acids. Age determination of fingermarks is invaluable with respect to forensic science, as the approximate time a fingermark was deposited can include or exclude potential suspects based on a time frame.