Method for characterization of adhesion properties of trace explosives in fingerprints and fingerprint simulations

The near inevitable transfer of explosive particulate matter through finger prints makes it possible to detect concealed explosives through surface sam pling. Repeatable and well-characterized fingerprint simulation facilitates quantitative comparison between particulate sampling methods for subsequen t detection of trace explosive residues. This study employs a simple, but r eproducible sampling system to determine the accuracy of a fingerprint simu lation. The sampling system uses a gas jet to entrain particles from a subs trate and the resulting airborne particles are then aspirated onto a Teflon filter. A calibrated Barringer IonScan 400 ion mobility spectrometer was u sed to determine the mass of explosive material collected on the filter. Th e IonScan 400 was calibrated with known masses of 2,4,6-trinitrotoluene (TN T). The resulting calibration curve is in good agreement with that obtained by Garofolo et al. (1994) (1) for an earlier model of the instrument. The collection efficiency of the sampling system was measured for three particl e sizes (8.0, 10.0, and 13.0 mu m) using spherical polystyrene particles la ced with known quantities of TNT. Collection efficiency ranged from less th an 1% for the larger particles to 5% for the smaller particles. Particle en trainment from the surface was monitored with dark field imaging of the rem aining particles. The sampling system was then applied to two C4 test sampl es-a fingerprint transfer and a dry Teflon transfer. Over 100 ng of RDX was collected from the dry transfer sample, while less than 1 ng was collected from the fingerprint transfer. Possible explanations for this large differ ence are presented based on the system calibration.