Method for Characterization of Adhesion Properties of Trace Explosives in Fingerprints and Fingerprint Simulations

• NCJ Number: 184323
• Journal: Journal of Forensic Sciences Volume: 45 Issue: 4 Dated: July 2000 Pages: 774-784
• Author(s): Denis J. Phares Ph.D.; Gregory T. Smedley Ph.D.; Richard C. Flagan Ph.D.; Jason K. Holt M.S.
• Date Published: July 2000
• Length: 11 pages
• Publication Format: Article
• Publication Type: Research (Applied/Empirical)
• Language: English
• Country: United States of America

Annotation

This study used a simple and reproducible sampling system to determine the accuracy of a fingerprint simulation to aid the quantitative comparison of particulate sampling methods used for the detection of trace residues of explosive particulates.

Abstract

The nearly inevitable transfer of explosive particulate matter through fingerprints makes it possible to detect concealed explosives through surface sampling. The sampling system in this study used a gas jet to entrain particles from a substrate; the resulting airborne particles were then aspirated onto a Teflon filter. A calibrated Barringer IonScan 400 ion mobility spectrometer was used to determine the mass of explosive material collected on the filter. The IonScan 400 was calibrated with known masses of 2,4,6-trinitrotoluene (TNT). Results revealed that the resulting calibration curve was in good agreement with that obtained by Garofolo and others in 1994 for an earlier model of the instrument. The study measured the collection efficiency of the sampling system for three particle sizes, using spherical polystyrene particles laced with known quantities of TNT. Collection efficiency ranged from less than 1 percent for the larger particles to 5 percent for the smaller particles. Dark field imaging of the remaining particles monitored particle entrainment from the surface. The sampling system was then applied to two C4 test samples: a fingerprint transfer and a dry Teflon transfer. More than 100 nanograms of RDX were collected from the dry transfer; less than from the fingerprint transfer. Findings demonstrated a system capable of subjecting particulate deposits to known aerodynamic shear stresses to study the forces binding micron sized particles of explosives to surfaces. However, improvement is needed at larger particle sizes where inertial effects limit the collection efficiency. Figures, tables, and 17 references (Author abstract modified)