Study of Conventional Preconcentration Techniques for Explosive Vapors.
Final rept. 23 Mar-15 Aug 73,
CALIFORNIA UNIV LIVERMORE LAWRENCE LIVERMORE LAB
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The performance of an explosive detector can be enhanced by preconcentrating the available explosive vapor prior to its introduction into the detector. Four conventional techniques - cryogenic trapping, adsorption on active surfaces, semipermeable membrane separation, and thermal cracking - were evaluated for the concentration of TNT vapors. Cryogenic trapping was found to be ineffective below 5 C because of an unexplained loss of TNT and interference by condensed water vapor. Various gas chromatographic column packing materials were tested to determine adsorption efficiency and temperature-cycle limits. They proved to be efficient traps for TNT, as did teflon and unprepared metal surfaces. These experiments were conducted using an electron-capture detector with argon5 percent methane as a carrier gas. Single-stage and two-stage membrane separators were interfaced with a quadrupole mass spectrometer, providing an enrichment of TNT concentration of 601 and 3501, respectively. However, problems were encountered with memory effects and a change in membrane permeability with thermal cycling. Finally, thermal cracking of TNT was expected to give a threefold enrichment of NOx relative to TNT concentration. A quartz tube and a copper tube were heated to 900 C and a TNT-bearing gas stream passed through each. However, no NOx was observed using a mass spectrometer. Of the systems examined, adsorption by metal surfaces and chromatographic packing materials appear most promising. Adsorption by metal surfaces has the additional advantages of reduced water interference, easier thermal cycling, reduced memory effects, and greater durability. Author
- Ammunition and Explosives
- Atomic and Molecular Physics and Spectroscopy