Investigations into Sampling Approaches for Chemical Analysis of Latent Fingermark Residue

Compositional variation of latent fingermark deposits sampled from the same donor (intra-donor) poses considerable challenges for the investigation of the degradation of chemical composition. The work presented here investigates the best approach of sampling of latent fingermark residues within this context. Gas chromatography-mass spectrometry (GC-MS) was used to quantify the amount of squalene in fingermarks deposited on non-porous surfaces and used it as an indicator of the amount of non-polar material successfully extracted. It was found that the percentage difference of squalene between two deposits (from two hands) obtained at a given time without controlling the deposition pressure was in the range of 4-100%. This was reduced to 0-44% in the other three sampling approaches, where deposition pressure was controlled. Under controlled deposition pressure, the averages of percentage difference (n=9) for sebum-rich and natural deposits were 13% and 20% respectively. These results demonstrate the significant influence of fingermark sampling approach over data and offer possible sampling strategies that can be undertaken to overcome issues associated with intra-donor variation.