Determination of the time-dependent change in the vapor concentration of 2,4,6-trinitrotoluene during the sublimation of its traces from the glass surface

The results of the measurements of 2,4,6-trinitrotoluene (TNT) vapor concentration over its trace amounts, called thin films, on the glass surface with a concentration of 100 ng/cm2 in a square area with a side of 1 cm over time are presented. The trace amounts of TNT on the glass were formed by applying a solution of TNT in the acetonitrile diluted with the chemically pure acetone, followed by the evaporation of the solvents. In order to measure the TNT vapor concentration, an EKHO-V-IDTS portable multibacillary gas-chromatograph with preliminary TNT vapor concentration was used. A sampling of the TNT vapor above the object was carried out with a remote vortex sampler. The vapor sample was taken from a distance of 2 cm from the glass surface. The concentration in the mode of the complete capture of TNT vapors was carried out to the stainless-steel wire mesh. The vapor concentration was determined from the chromatographic peak amplitude. It was found that the concentration of vapor over the examined surface with an area of 1 cm2 decreases from 10-13 to 10-14 g/cm3 within 2.6 ± 0.3 hours. TNT vapor concentration value of 10-14 g/cm3 corresponds to the threshold concentration of TNT vapor for the modern detectors. Based on the assumption that the vapor concentration is proportional to the amount of the TNT mass on the surface for the considered trace amounts of TNT, it was estimated that the initial surface concentration of trinitrotoluene of 100 ng/cm2 on the glass surface decreases to 12 ng/cm2 within 2.6 ± 0.3 hours due to sublimation into an open half-space. It was shown that the use of vortex sampling of vapor intensifies the sublimation of TNT from the glass surface.

Effect of Initial Surface Concentration on Bacterial Distribution in a Surrogate Ballistic Wound

In ballistic injuries, contamination can be carried from the environment, clothing, and skin surface into the wound track. Bacteria and contaminated debris can be introduced into the wound by several means, including physical transport by the projectile or by the suction caused by the formation and collapse of the temporary wound cavity. In this paper, the relationship between initial bacterial concentration on the surface and resultant bacterial distribution along the wound channel is examined using a leg surrogate. Escherichia coli strain K-12 was used to represent skin surface contamination. In order to reduce the possibility of contamination by outside bacteria and assist in colony visualization, the E. coli first underwent a transformation protocol to express Green Fluorescent Protein and to be resistant to the antibiotic ampicillin. Different concentrations of bacteria were pipetted onto circular filter paper and placed onto the surface of a ballistic gelatin leg surrogate, and an 11.43-mm (0.45-in) caliber projectile was shot through the contaminated area into the gel. The “wound track” was sliced into small, evenly spaced samples and the permanent cavity was removed using a biopsy punch, liquefied, and grown on selective lysogeny broth media containing ampicillin. Examination of a normalized bacterial colony count and normalized area covered per segment allowed comparison of variations in the initial concentration, and confirmed that within a range the normalized contamination distribution trend along the “wound track” remained similar. This verification allowed additional confidence in results obtained using this bacteria distribution methodology by eliminating concerns over small variations in initial bacterial concentration.

Optimization of the Self-Quenching Response of Nitrobenzoxadiazole Dipalmitoylphosphatidylethanolamine in Phospholipid Membranes for Biosensor Development

Incorporation of the lipid-conjugated fluorescent probe nitrobenzoxadiazole dipalmitoylphosphatidylethanolamine (NBD-PE) into bilayer lipid membranes (BLMs) provides a matrix wherein changes in the structure of the membrane can be transduced into changes in fluorescence intensity or lifetime. In the work reported here, a comparison was made between an empirical model recently developed by our group to account for alterations in the fluorescence lifetime and average fluorescence intensity of NBD-PE as a result of self-quenching and an earlier alternative model which describes self-quenching of membrane-bound chlorophyll a. Our model showed the more satisfactory correlation with self-quenching data obtained from lipid membranes containing 1 to 50 mol % of NBD-PE. This model was used to determine the optimum initial surface concentration of NBD-PE to be incorporated into phospholipid membranes for biosensor development. Optimization was based on the magnitude of the change in fluorescence intensity as a function of changes in the local concentration of the probe. The presence of acidic headgroups in the membrane results in negligible improvement in sensitivity, while a heterogeneous membrane structure greatly enhances the signal magnitude. Experimental results did not provide accurate optimum concentrations, although two NBD-PE surface concentrations were found to yield close agreement with theoretically predicted optimum surface concentrations of 0.027 ± 0.001 and 0.073 ± 0.001 molecules NBD-PE nm−2.