Explosives, electron-capture detection

J.M.P. Douse, Trace analysis of explosives at the low nanogram level in handswab extracts using columns of Amberlite XAD-7 porous polymer beads and sdica capillary column gas chromatography with thermal energy analysis and electron capture detection , J. Chromatogr., 328 (1985) 155-165. 

J. M. F. Douse, Trace Analysis of Explosives in Handswab Extracts Using Amberlite XAD-7 Porous Polymer Beads, Silica Capillary Column Gas Chromatography with Electron Capture Detection and Thin Layer Chromatography, Journal of Chromatography 234 (1982) 415. 

Douse JMF. 1982. Trace analysis of explosives in hand-swab extracts using Amberlite XAD-7, porous beads, silica capillary-column gas chromatography with electron-capture detection and thin-layer chromatography. J Chromatogr 234 415-425. 

An improvised chlorate-nitrobenzene binary explosive formerly used by terrorists in the UK was abandoned because its presence was suggested by the persistent odor of nitrobenzene (NB) both on the clothing of the handlers of the explosive and in the postblast debris. Relatively low levels of NB are easily detectable by vapor sampling and GC with electron capture detection. Commercial nitromethane (NM) binary types will probably exhibit little residual NM postblast, but container fragments may permit detection of the liquid absorbed into the plastic. 

Traces of explosives are commonly present in very low levels in samples that are analysed, so it is important to take sensitivity into account when designing detectors for explosive detection. As a rough rule of thumb , Nambayah and Quickenden [38] reported that a method suitable for direct explosive vapour detection should be able to detect explosive concentrations at less than 1 ng/L. They made an exhaustive study of the lowest experimental detection limits achieved with various analytical techniques reported in the literature on traces of explosive, and they informed that headspace GC-electron capture detector (ECD) followed by immunosensor techniques achieves the lowest detection limits (from 0.07 to 20 ng/L). 

GC is used for the detection and identification of explosives, whether they are found as pure materials or postblast residues. According to Yinon and Zitrin, GC detectors suitable for the determination of explosives are the F.I.D., mass spectrometer (MS), electron capture detector (ECD), nitrogen-phosphorus detector (NPD), and thermal energy analyzer (TEA). The most selective detector is the TEA, which detects only compounds that produce NO or NO2. 

A wide variety of other MS techniques are used to detect explosives. Two notable techniques are Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and CE-MS. FT-ICR-MS is used to probe pseudomolecular ion formation of RDX, PETN, and TNT using several ionization sources including EDI, El, electron capture ionization (EC), and chemical ionization (Cl). Analyses are performed both in the positive and negative ionization mode, and identities are assigned to the major pseudomolecular ion peaks seen in the spectra from each explosive [198]. TTie composition of several explosive compounds from postblast residue is assessed with FT-ICR-MS by identifying the explosive and inactive ingredients in a smokeless powder, TNT,... 

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