Surface wipe-sampling

After dry-transfer, the test surface was adhered to the translatable platen of the TL-slip/peel tester or to the xy-platform of the robo3D wipe-sampler with double sided tape. A single strip of tape was placed perpendicular to the sampling path and was used to secure the edge of the test surface where the sampling path began. This allowed for the fabrics (ballistics nylon and synthetic leather) to stretch along the wipe path and prevented them from bunching up during the wipe-sampling. The collection wipe was secured in the wipe mount system with a circular 3 cm diameter section exposed for collection. The wipe mount was positioned to initially meet the test surface and immediately pass through the area of dry-transfer (Figure 2). The selected steel weight was attached to the top of the mount and the mount or test surface was translated to collect the RDX deposit. All experiments were repeated with a minimum of six trials and used the following wipe-sampling conditions unless otherwise noted: dry-transfer of 350 ng deposits of RDX, a Nomex® wipe, a translational velocity of 5 cm s⁻¹, an applied load of 660g, and a linear travel distance of 12 cm.

ABS plastic and ballistics nylon surfaces were investigated using the TL-slip/peel tester or the Robo3D with an applied load of 660 g for ABS plastic or 1060 g for ballistics nylon.

ABS plastic, ballistics nylon, cardboard, packaging tape (a single piece of packaging tape placed over a strip of cardboard), synthetic leather, and stainless steel (sampling path parallel to step heights) were investigated using the Robo3D.

ABS plastic, synthetic leather, and ballistics nylon were investigated using the Robo3D and an applied load of 260 g, 460 g, 660 g, 860 g, or 1060 g.

ABS plastic was investigated using the Robo3D and a linear travel distance of 5 cm, 12 cm, or 20 cm.

ABS plastic was investigated using the Robo3D and a Nomex® or Teflon wipe, an applied load of 260 g, 460 g, 660 g, 860 g, or 1060 g with the following test surface modifications (Figure 5 schematic): artificial sebum/modified fingerprint mixture not added (None), 2 μL artificial sebum (2 μL AS) prepared using the protocol recently developed by Sisco et al.,⁵¹ 10 μL artificial sebum (10 μL AS), or 10 μL of a modified fingerprint mixture (10 μL MFM) comprised of 200 μL squalene, 200 μL palmitoleic acid, 50 mg pentadecanoic acid in 6 mL hexane.

Comparison (left) of collection efficiencies of RDX using Nomex® wipes and the Robo3D wipe-sampler for different test surface conditions: artificial sebum/modified fingerprint mixture not added (None), addition of 10 μL of artificial sebum (10 μL AS), and addition of 10 μL of modified fingerprint mixture (10 μL MFM). Uncertainties represents one standard deviation of the mean. Schematic (right) for wipe-sampling: (A1) first pass of the sample path, (B1) footprint of wipe start location for the first pass, (E) location of the added artificial sebum or modified fingerprint mixture, (D1) footprint of wipe end location for first pass, (A2) second pass of the sample path, (B2) footprint of wipe start location for the second pass, (C) dry-transfer location of analyte particles, (D2) footprint of wipe end location for second pass.

ABS plastic was investigated using the Robo3D and a total travel distance of 12 cm following a single 12 cm line, an L-shape (6.0 cm per side), a U-shape (4.0 cm per side), or a square (3.0 cm per side) (Figure 6 schematic). To remove any effect from the hair-cell texture of the ABS plastic, the patterns were sampled in two orientations (0° and 90°).

Schematic (top) for wipe-sampling (A) sample path, (B) footprint of wipe start location, (C) dry-transfer location of analyte particles, (D) footprint of wipe end location. Wipe patterns include (I) single 12 cm line, (II) L-shape with 6.0 cm per side, (III) U-shape with 4.0 cm per side, and (IV) square with 3.0 cm per side. Graph (bottom) of collection efficiencies of RDX using Nomex® wipes for these sample paths and orientations of the hair-cell pattern of ABS plastic using a Robo3D wipe-sampler. Uncertainties represent one standard deviation of the mean.

ABS plastic was investigated using the Robo3D and a total travel distance of 20 cm in a linear or a 47 cm × 30 cm serpentine pattern (Figure 7 schematic).

Schematic (top) for wipe-sampling (A) sample path, (B) footprint of wipe start location, (C) dry-transfer location of analyte particles, (D) footprint of wipe end location. Sampling paths include (I) single 20 cm line, (II) 4.7 cm × 3.0 cm serpentine, (III) 3 lines, 6.7 cm each, (IV) 4 lines, 5.0 cm each, and (V) 5 lines, 4.0 cm each. Graph (bottom) of collection efficiencies of RDX using Nomex® wipes for these sampling paths across ABS plastic using a Robo3D wipe-sampler. Uncertainties represent one standard deviation of the mean.

ABS plastic was investigated using the Robo3D and a total travel distance of 20 cm following a single 20 cm line, three 6.7 cm lines, four 5.0 cm lines, or five 4.0 cm lines (Figure 7 schematic).