Comparison of Derivatization Methods for Groomed Latent Print Residues Analysis via Gas Chromatography

Abstract

The practice of latent print analysis is comprised of a visual examination and the comparison of the fingerprint pattern from a questioned print to an exemplar(s). When a questioned print is either smudged or contains little pattern detail, the print comparison would be considered an inconclusive determination. However, in these scenarios, the latent print residues (LPRs) could provide associative information to supplement the current ACE-V (Analysis, Comparison, Examination-Verification) process. Advancements using analytical techniques allow for the analysis of LPR chemistry; however, derivatization is generally required to increase the abundance of components not traditionally observed in gas chromatography. This study aimed to determine whether two derivatization reagents, boron trifluoride in methanol (BF3-MeOH) and N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA), provide a better recovery of LPR components from a porous or non-porous substrate. Five volunteers deposited groomed latent print samples onto two substrates: a microfiber filter (porous) and a microscope slide (non-porous). The residues were derivatized or evaporated prior to the gas chromatography-mass spectrometry (GC-MS) analysis. The percent recoveries were higher, >83%, in the DCM extracted samples for both substrates compared to those samples prepared in hexanes. DCM/MSTFA derivatization provided the recovery of fatty acids that ranged from 20 to 30% for both substrates and a recovery of squalene at a rate of 2.37% for the filter sample and 4.2% for the slide sample. These rates were higher than the recovery rates obtained for the hexanes/BF3-MeOH-derivatized samples, with a range of 1–8% for the fatty acids recovery rates and 0.6–0.85% for squalene from both substrates. Overall, the MSTFA derivatization reagent produced higher recoveries for LPR on porous and non-porous substrates while providing a LPR chromatographic profile similar to that of a non-derivatized sample. The use of DCM as a solvent provided a wider range of LPR components recovered than hexanes and, thus, should be used as the extraction solvent when derivatizing samples, regardless of the substrate.