Effect of re-use of surface sampling traps on surface structure and collection efficency for trace explosive residues.

In security settings, explosive residues or particles are collected by swiping the object of interest (e.g., luggage or package) with a collection medium, or trap. Particles on the trap are thermally desorbed for detection by ion mobility spectrometry (IMS) or other analyses. A high trap sampling efficiency increases the chance of detection, and is affected by a number of factors. In particular, this work studies the effect of trap re-use on collection efficiency of organic explosives, namely 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazinane (RDX), and correlates this data to quantifiable morphology changes. Collection efficiency was measured by liquid extraction of the traps with detection and quantitation by gas chromatography / mass spectrometry (GC/MS). Using silhouette microscopy for visualization of the trap texture, morphology changes were quantified by several measurements of trap roughness and hairiness, drawing from techniques and metrics used in the textiles industry. Nomex traps were visibly roughened by repeated re-use, and this was correlated with significant improvements in trap collection efficiency (11-57%) depending upon the specific analyte and substrate combination interrogated. Teflon-coated fiberglass (TCFG) traps showed little change with repeated swiping and minimal to no improvement in particle collection efficiency. These results have direct implications for optimizing particle collection traps for use in security settings.