changes of the lipid composition with time [40] suggested that the short chain fatty acids concentration increase in the first 15 days due to degradation of the longer chain fatty acids – C14 concentration initially increases in the first 20 days followed by a decrease down to original or lower levels. Shortening the hydrocarbon chains of the fatty acids to octanoic (C8) and nonanoic (C9) acids which are found in greater concentration in aged fingermarks and are further subject of break down and evaporation was discussed in the US Department of Justice Fingerprint Sourcebook [3]. These fatty acids are in liquid form in the temperature range of this experiment and could migrate easily. The liquid fatty acids concentration could be also increased by hydrolysis of triglycerides which delivers a mixture of saturated and unsaturated fatty acids [47]. Some of the low weight degradation products of squalene such as acetone [38,41] could serve as strong solvents for the solid components which can cause further liquidation of the ridge deposit and easier migration on the surface. It is also important to notice the hydrophilic nature of this surface which can cause significant horizontal spreading of liquid fatty acids. On the other hand unsaturated compounds such as unsaturated fatty acids and squalene tend to form oxidized solid products such as hydroperoxides or epoxides. Polymerization of unsaturated compounds by carbon-carbon bonds formation can also create waxy solid [38,40]. However the lower molecular weight and unsaturated compound migration hypothesis needs high resolution chemical analysis in order to be confirmed. A recent study demonstrated that fingermark material in vacuum migrates across a surface - moving from ridge to ridge, a few hundred micrometres, in four days [34]. However, this study utilizes time of flight secondary ion mass spectrometry (TOF-SIMS) to image the fingermark changes. This is a high vacuum technique which is likely to increase the mobility of material on the surface and may not be directly applicable to migration of the mark components in air. The component shown to migrate in the ToF-SIMS study, palmitic acid, is solid at room temperature and pressure and whilst may be a component of the intermediate layer along with unsaturated or lower molecular weight products, is unlikely to fully explain the development of intermediate area in ambient conditions.
changes of the lipid composition with time [40] suggested that the short chain fatty acids concentration increase in the first 15 days due to degradation of the longer chain fatty acids – C14 concentration initially increases in the first 20 days followed by a decrease down to original or lower levels. Shortening the hydrocarbon chains of the fatty acids to octanoic (C8) and nonanoic (C9) acids which are found in greater concentration in aged fingermarks and are further subject of break down and evaporation was discussed in the US Department of Justice Fingerprint Sourcebook [3]. These fatty acids are in liquid form in the temperature range of this experiment and could migrate easily. The liquid fatty acids concentration could be also increased by hydrolysis of triglycerides which delivers a mixture of saturated and unsaturated fatty acids [47]. Some of the low weight degradation products of squalene such as acetone [38,41] could serve as strong solvents for the solid components which can cause further liquidation of the ridge deposit and easier migration on the surface. It is also important to notice the hydrophilic nature of this surface which can cause significant horizontal spreading of liquid fatty acids. On the other hand unsaturated compounds such as unsaturated fatty acids and squalene tend to form oxidized solid products such as hydroperoxides or epoxides. Polymerization of unsaturated compounds by carbon-carbon bonds formation can also create waxy solid [38,40]. However the lower molecular weight and unsaturated compound migration hypothesis needs high resolution chemical analysis in order to be confirmed. A recent study demonstrated that fingermark material in vacuum migrates across a surface - moving from ridge to ridge, a few hundred micrometres, in four days [34]. However, this study utilizes time of flight secondary ion mass spectrometry (TOF-SIMS) to image the fingermark changes. This is a high vacuum technique which is likely to increase the mobility of material on the surface and may not be directly applicable to migration of the mark components in air. The component shown to migrate in the ToF-SIMS study, palmitic acid, is solid at room temperature and pressure and whilst may be a component of the intermediate layer along with unsaturated or lower molecular weight products, is unlikely to fully explain the development of intermediate area in ambient conditions.
PopovSearsJones_Migration_Fingerprints_NonPorous_AFM_Archive_Version.docx