A new wipe-sampling instrument for measuring the collection efficiency of trace explosives residues

Abstract

Trace explosives detection, a crucial component of many security screening environments, commonly employs wipe-sampling. Since collection of an explosive residue is necessary for detection, it is important to have a thorough understanding of the parameters that affect the efficiency of collection. Current wipe-sampling evaluation techniques for explosive particles have their limits: manual sampling (with fingers or a wand) is limited in its ability to isolate a single parameter and the TL-slip/peel tester is limited to a linear sample path. A new wipe-sampling instrument, utilizing a commercial off-the-shelf (COTS) 3D printer repurposed for its XYZ stage, was developed to address these limitations. This system allowed, for the first time, automated two-dimensional wipe-sampling patterns to be studied while keeping the force and speed of collection constant for the length of the sampling path. This new instrument is not only capable of investigating the same parameters as current technology (wipe materials, test surfaces, forces of collection, and linear sample patterns), it has added capabilities to investigate additional parameters such as directional wipe patterns (i.e. "L" and "U" shapes, square, and serpentine) and allowing for multiple lines to be sampled during a single collection without the need for adjustments by the user. In this work, parametric studies were completed using 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and the COTS 3D printer for wipe-sampling to establish collection efficiencies for numerous scenarios. Trace explosives detection in field screening environments could be greatly improved with the ability to comprehensively investigate how a wide range of parameters individually affect collection by wipe-sampling. A screener who knows how to properly interrogate any given surface will be much more efficient at detecting trace explosives.

Improving particle collection efficiency of sampling wipes used for trace chemical detection

“…Experimental details for these procedures may be found in several recent publications. 12–14 Briefly, explosive particle deposits were inkjet printed as 8 × 8 spot liquid droplet arrays, with a total mass loading of 350 ng, onto 1 cm by 1 cm square Bytac strips (Teflon film with foil backing, BytacBench and Shelf Protector Sheets, SPI Supplies and Structure Probe, West Chester, PA) using a JetLab 4XL inkjet printer (MicroFAB, Plano, TX) and a 1 mg mL −1 acetonitrile standard solution of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) (Cerilliant Corp., Round Rock, TX). After printing, the arrays were dried to create solid explosive particle residues which were then transferred to the test surface using a dry transfer protocol.…”

“…A robotic wipe-sampling instrument, based on a repurposed Robo3D fused deposition modelling (FDM) printer (Robo3D, San Diego, CA), was used to complete the swiping experiments as a function of the mass placed on the mount holding the sampling wipe with values ranging from 260 g to 1060 g (applied load of 2.6 N to 10.4 N) using a translational velocity of 5 cm s −1 over a total travel distance of 12 cm. 14 Both this and the Bytac strip used for manual deposition of the explosive particles onto the test surface and the wipe (TCF or CN) were set aside for quantitation. Previous results have demonstrated that the slip/peel tester described previously, and the robot sampling system (which uses the same mounting hardware) provide equivalent results.…”

“…Previous results have demonstrated that the slip/peel tester described previously, and the robot sampling system (which uses the same mounting hardware) provide equivalent results. 14…”

“…The extracts were then transferred to 2 mL amber vials for analysis by ESI-MS using a Thermo Scientific UltiMate 3000 LC system (Thermo Scientific, Waltham, MA) coupled to a JEOL JMS-T100LP time-of-flight mass spectrometer (JEOL USA, Peabody, MA) using experimental conditions described elsewhere. 14…”

In Situ Visualization of Particle Motions during Wipe Sampling of Explosives and Other Trace Particulate Materials

“…Effective wipe- or swab-based processes for the removal of particulate matter from surfaces are important for applications such as trace contraband detection, − toxic substance sampling, − and dust removal and cleaning. − In many applications, ineffective particle collection can have serious repercussions, including national security risks (failure to detect explosives at security checkpoints) and public health emergencies (failure to detect chemical warfare agents or toxic metals). Despite these consequences, wipes used in trace detection typically collect only a small fraction of particles present on a given surface.…”