A method to determine collection efficiency of particles by swipe sampling

Abstract

A methodology was developed to evaluate particle collection efficiencies from swipe sampling of trace residues. Swipe sampling is used for many applications where trace residues must be collected, including the evaluation of radioactive particle contamination and the analysis of explosives and contraband at screening checkpoints using ion mobility spectrometry (IMS). Collection efficiencies were evaluated for micrometer-sized polystyrene latex (PSL) spheres with respect to the particle size and mode of deposition, collection trap, surface type and swiping force. Test surfaces containing particles were prepared under controlled conditions and swiped with a reproducible technique that allows for the evaluation of frictional forces. Collection efficiencies were determined by optical imaging and particle counting. Of the two IMS collection traps studied, the polytetrafluoroethylene (PTFE) trap has significantly lower collection efficiencies. This is likely to be due to a combination of texture and composition. The larger (42 μm diameter) particles are collected more efficiently than the smaller (9 μm diameter) particles. Particles in a matrix similar to latent fingerprints are collected more efficiently than dry particles. Applying greater force during swiping does not greatly improve collection efficiencies. This fact, coupled with the observation that many particles are detached but not collected, implies that improvements in collection efficiency are dependent on improvements in adhesion of the particles to the collection surface, rather than larger forces to detach the particles.

Inkjet Metrology: High-Accuracy Mass Measurements of Microdroplets Produced by a Drop-on-Demand Dispenser

“…Small volume dispense technologies are also used for precise and accurate delivery of fluid volumes in miniaturized analytical assays, 10−18 microfluidic chips,(19) microelectromechanical system devices,(20) olfactometers,(21) vapor generators,(22) and trace reference materials. (23) In large part, the limitations and uncertainties inherent in these applications are due to practical difficulties associated with determination and control of the size of the dispensed aliquots. These practical difficulties include subtle changes in operational and environmental variables, and physicochemical changes around the dispense orifice that can influence mass delivery.…”

Broad spectrum infrared thermal desorption of wipe-based explosive and narcotic samples for trace mass spectrometric detection

“…A similar artificial fingerprint laden with 2 μg of each PETN and ETN was deposited and swiped for analysis in negative mode at 50% power for a 10 s duration. The collection efficiency of the PTFE-coated fiberglass wipes used here was on the order of single percentages as demonstrated in prior work, 38,39 estimating detection levels of single to tens of nanograms for the exogenous compounds. The nitrate adducts of both explosives were observed (Fig.…”

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics

“…In the following, we extend colloidal-probe AFM to assess the adhesion between explosives and different fabric types. Explosive/fabric adhesion studies are vital, not only because they provide information regarding a particle’s affinity for clothing, but also may enable insight into the efficacy of different detection schemes [56]. …”