CHARACTERIZATION OF SEMTEX BY SUPERCRITICAL FLUID EXTRACTION AND OFF-LINE GC-ECD AND GC-MS

Researchers using electron capture for the detection of explosive vapors currently claim the ability to detect the presence of RDX in Semtex - a plastic explosive comprising hexahydro-1,3,5-trinitro-1,3,5-triazane (RDX) in a matrix of styrene-butadiene copolymer and hydrocarbon oil. The vapor pressure of RDX at room temperature is 0.006 ppb, and therefore well below the detection limit of electron capture detection (ECD). The positive response generated by ECD is, consequently, not from the presence of RDX, but from some other component. This paper describes the extraction and identification of several compounds in Semtex, along with the determination of which is responsible for the positive response of an ECD-based detector. From the results of supercritical fluid extraction and off-line gas chromatography combined with electron capture and mass spectrometric detection, it has been concluded that ethylene glycol dinitrate is the component responsible for the positive ECD response. This conclusion is based on the requirements necessary for ECD detection, i.e. electronegativity, and a sufficient vapor pressure. The other compounds present were eliminated as possible choices because they either can not be detected by an ECD or do not have sufficient vapor pressure under ambient conditions.