TNT Vapor Research Articles

Photodissociation followed by laser-induced fluorescence at atmospheric pressure and 24 °C: a unique scheme for remote detection of explosives

A unique scheme has been applied for sensitive remote detection of 2,4,6-trinitrotoluene (TNT) vapor trace amounts at atmospheric pressure and 24 degrees C. The detection concept is based on a single laser beam inducing a tandem process: photodissociation of TNT vapor followed by highly selective detection of its photofragments vibrationally excited NO, utilizing laser-induced fluorescence with the A2Sigma+(v' = 0) <-- X2Pi(v'' = 2) transition. A detection sensitivity of at least 8 parts in 10(9) of TNT vapor with a signal-to-noise ratio of approximately 10 has been experimentally verified for an unfocused approximately 5-mJ laser beam, measured at a distance of approximately 15 cm from the TNT sample.

Optical Properties of Gaseous 2,4,6-Trinitrotoluene in the Ultraviolet Region

The absorption spectrum of gaseous 2,4,6-trinitrotoluene (TNT) was recorded by conventional absorption spectroscopy (AS) as well as cavity ringdown spectroscopy (CRDS) methods in the spectral regions 195–300 and 225–235 nm, respectively. These spectra were normalized by using the saturated TNT vapor-number density for the measured cell temperature to obtain the absorption cross section of TNT. No spectral features were found in the spectra; this result is consistent with a repulsive electronic excited state of TNT. The temperature dependence of the absorption coefficient of saturated TNT vapor was measured within the temperature range 5–110 °C. The limit of detection of TNT vapor by CRDS is less than 1 ppb. Real-time CRDS measurements of the TNT vapor density at 21 and 37 °C are presented. The TNT evaporation rates were found to be 7 × 108 and 4 × 1010 molecules/cm2 × s at 21 and 37 °C, respectively.

Detection of nitrobenzene, DNT, and TNT vapors by quenching of porous silicon photoluminescence

The detection of nitroaromatic molecules in air by the quenching of the photoluminescence of porous silicon (porous Si) films has been explored. Detection is achieved by monitoring the photoluminescence (PL) of a nanocrystalline porous Si film on exposure to the analyte of interest in a flowing air stream. The photoluminescence is quenched on exposure to the nitroaromatic, presumably by an electron-transfer mechanism. Detection limits of 500 parts-per-billion (ppb), 2 ppb, and 1 ppb were observed for nitrobenzene, 2.4-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT), respectively (exposure times of 5 min for each, in air). Specificity for detection is achieved by catalytic oxidation of the nitroaromatic compound. A platinum oxide (PtO2) or palladium oxide (PdO) catalyst at 250 degrees C. placed in the carrier gas line upstream of the porous Si detector, causes oxidation of all the nitroaromatic compounds studied. The catalyst does not oxidize benzene vapor, and control experiments show no difference in the extent of PL quenching by benzene with or without an upstream catalyst. The PL quenching by NO2, released in the catalytic oxidation of nitroaromatic compounds, is less efficient than the quenching of the intact nitroaromatic compound. This provides a means to discriminate nitro-containing molecules from other organic species.

Porous Shape Persistent Fluorescent Polymer Films: An Approach to TNT Sensory Materials

Fluorescence is a leading signal transduction method for the formation of chemosensory devices.1,2 Conjugated polymer-based fluorescent chemosensors have been proven to further amplify this inherently sensitive method.2 Although solid-state (thin film) fluorescent chemosensory devices are generally required, most systems have limited solid state utility with the lack of stable (reproducible) spectroscopic features and low fluorescence quantum yields, presumably due to the excimer formation and selfquenching.3,4 These processes have been an impediment to other applications of conjugated polymers and general solutions also have implications for electroluminescent polymer devices.4 We report herein an approach to stable fluorescent conjugated polymer films by the incorporation of the rigid three-dimensional pentiptycene moieties,5 1, which prevent π-stacking or excimer formation. In comparison to the planar model polymer 3, thin films of the pentiptycene polymer, 2, display enhanced fluorescence quantum yield and stability. Moreover, their potential for the trace detection of high explosives such as 2,4,6-trinitrotoluene (TNT) is also reported.6 Polymer 2 has unprecedented high sensitivity as an artificial fluorescent chemosensor for the vapors of TNT and 2,4-dinitrotoluene (DNT).

Surface Contamination by TNT

Abstract We have performed experiments that indicate TNT contamination is present on surfaces exposed to TNT vapor, and that TNT contamination is transferred rapidly between proximate surfaces. Contaminated surfaces continue to be nearly constant sources of TNT vapor for some time after removal of the primary source.

TNT vapour measurements above buried landmines. Model experiments using [methyl-14C] TNT

Abstract As many land-mines are no longer made of metallic substances, locating mines by detection of the vapour of explosives has been proposed as an alternative. In order to set a goal for these detectors a required detection limit was generated. The vapour concentration of TNT above buried land-mines was estimated using model experiments with radioactive labelled TNT, which was synthesized for this purpose. When burying TNT sealed in PVC under a 6 cm thick layer of soil after 50–60 hours breakthrough of TNT vapours was observed. Extrapolating from these measurements to a real minefield situation yielded concentrations in the sub-ppt range inside as well as in the neighbourhood of the field.

The use of a solid sorbent as a collection medium for TNT and RDX vapors

A method is presented for sampling atmospheric vapors of the military explosives, TNT and RDX, with sorbent tubes containing Tenax-GC resin. Vapors were produced by placing TNT and RDX in a heated glass chamber and pulling the generated vapors on to the Tenax with an air sampling pump. Collection efficiencies were determined for concentrations of 2,1,0.5, 0.25, and 0.1 times the Threshold Limit Values recommended by the American Conference of Governmental Industrial Hygienists. Electron capture gas chromatography was used for the analyses and quantitation of the collected explosives.