Postblast residues, detection

With a focus on trace forensic detection of explosives, especially for use in counterterrorism and to counter narcotics investigations, Fetterolf et al. [75] evaluated the use of ion mobility-mass spectrometry for explosives determinations. In this, explosives residues were collected on a membrane filter by a special attachment on a household vacuum cleaner. Although subsequent thermal desorption and analysis required only 5 s, fimits of detection for most common explosives were as low as 200 pg. The persistence of explosives on hands and transfer to other surfaces were also examined as were post-blast residues of NG on fragments of improvised explosive devices constructed with double-based smokeless powder. Finally, postblast residue from C-4, Semtex, and other explosives was found by IMS analyses on items of forensic and evidentiary value. These few out of many examples demonstrate that mobihty spectrometers are well suited tools for laboratory and on-site investigations, before and after the use of explosives. 

The analysis of explosives has rather obvious forensic implications. HPLC applications have been published concerning both the analysis of postblast residues in the attempt to identify the explosive used, and the detection of explosive traces on the hands and clothing of a suspect in order to provide... 

The simultaneous detection of small cations (ammonium, sodium, potassium, calcium, magnesium, and strontium) and anions (bromide, chloride, nitrite, nitrate, sulfate, perchlorate, thiocyanate, and chlorate) from low explosives in postblast residue using an elaborate electrolyte composed of a cationic chromophore and modifiers (imidazole/HIB A/18-crown-6 ether/ACN), an anionic chromophore (1,3,6-naphthalenesulfonic acid) and flow reversal agent (tetramethylammonium hydroxide) has been presented. " ... 

The detection of explosives and propellants in postblast residues and in hand swabs from persons suspected of firing a gun or handling explosives is extremely important for the success of a prosecution. The role of GC for the analysis of these polar and... 

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,... 

Identification of postblast residues of explosives is also an important analytical challenge [9]. In the forensic science field, the postblast residues adhering to samples are extracted using an organic solvent and the solution is analyzed by GC/MS. However, faster identification of the explosives used in a bombing would lead to faster apprehension of the perpetrators. We conducted tests to detect postblast residues by using the MS-based explosives detector without any pretreatment of the samples. 

Figure 21.17 shows the detection results of the postblast residues adhering to a cloth sample produced by the explosion of dynamite. As shown in Figure 21.17, the components of dynamite (i.e., ethylene glycol dinitrate [EGDN] and NG) were detected from the tested sample. 

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. 

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