Sampling techniques explosives analysis

Raman spectroscopy in the 1960s. The implementation of FT spectrometers and lasers with output wavelengths that minimized sample fluorescence increased the utility of the technique and fostered application to explosive analysis. 

The analytical methods currently used by this laboratory are chromatography (GC/TEA HPLC/PDME) for explosive residues and the particle analysis method (SEM/EDX) for FDR. The latter method involves the detection and identification of individual FDR particles therefore any sampling technique must be nondestructive. 

While IMS and MS are both widely used for explosives analysis, hybrid IM-MS instruments have recently been applied to detect explosives [186]. The lack of HLS-related research with IM-MS systems may be in part due to the availability of commercial IM-MS systems [183,187]. However, this hybrid technique offers a distinct advantage over both IMS and MS alone the ability to simultaneously separate samples by both mobility and mass. This twofold separation mechanism greatly decreases the likelihood of a mass or mobility interfer-ent masking the signal of the analyte of interest. In complex, real-world samples where matrix effects may significantly inhibit the detection of trace amounts of explosive material, the ability to separate in two dimensions (2D) is extremely powerful [188]. Figure 20.16 shows a typical 2D IM-MS plot of black powder with... 

High-performance liquid chromatography, or HPLC, is an analytical technique capable of detecting specific components in a sample. In forensic science this test is used for drug analysis, toxicology (study of poisons), explosives analysis, ink analysis, fibres and plastics. 

One of the most elusive explosives in postexplosion analysis is TATP. Used in many terrorist attacks, sometimes in large quantities by suicide bombers in public buses or crowded markets, it nevertheless was not identified in the debris (its presence was later learned from intelligence sources). A probable reason for the failure to identify TATP may be its high volatility. This was supported by an experiment in which TATP was allowed to explode and its residues were analyzed by GC-MS. Successful identification was achieved only if the extraction was carried out immediately after the blast [52]. Therefore, sampling techniques other than classical extraction were tried [53] direct analysis of the explosive vapors ( headspace ) and adsorption of the vapors on solid adsorbents. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

Comparison of Various FNAA Techniques for Assay of Synthetic Octol Samples Precision of Single-Axis Rotation FNAA for Assay of Octol Plant Samples Fast Neutron Activation Analysis for Nitrogen in Explosives by... 

A first approach to determining explosives on-site might include a combination of specialized sample-collection techniques and subsequent analysis using established IMS technologies or instruments. A second level of development could involve the fabrication of analyzers or analytical systems for an on-site operation and real-time analysis of samples. During the past several years, the first step of development has been demonstrated for explosives in water, in soils, and in a few unique uses. 

Techniques which may be used for coUection of trace explosives residues at a scene include swabbing with either dry or solvent wetted swabs, sweeping up dust and smaU particles into suitable receptacles, vacuum collection, and the use of a contact heater to coUect semi-volatile materials. If a bomb crater can be located, then samples of the soil from the crater should be sealed in nylon bags for later laboratory analysis. 

One can view samples from an explosion scene as belonging to one of two work streams (i) clean and (ii) dirty. Separation between these work streams needs to be established at the earliest possible moment in the process with appropriate laboratory facilities to handle each. The clean work stream contains items which are to be examined for invisible chemical traces of explosives. Such items need protection from any external contamination to a degree commensurate with the sensitivity of the chemical analysis techniques to be employed. The dirty work stream contains items that do not require trace analysis precautions, e.g., scene debris for physical searching. Nonetheless, such items still need to be handled in a way which protects their evidential integrity. Some items can start in the clean stream and then be transferred to the dirty stream, e.g., damaged motor vehicles may first be examined for explosive traces, and then transferred out of the trace examination area to be searched for physical evidence. 

Thermogravimetric analysis (TGA) is a suitable technique for the study of explosive reactions. In TGA the sample is placed on a balance inside an oven and heated at a desired rate and the loss in the weight of the sample is recorded. Such changes in weight can be due to evaporation of moisture, evolution of gases, and chemical decomposition reactions, i.e. oxidation. 

Interfacing the TEA to both a gas and a HPLC has been shown to be selective to nitro-based explosives (NG, PETN, EGDN, 2,4-DNT, TNT, RDX and HMX) determined in real world samples, such as pieces of explosives, post-blast debris, post-blast air samples, hand swabs and human blood, at picogram level sensitivity [14], The minimum detectable amount for most explosives reported was 4-5 pg injected into column. A pyrolyser temperature of 550°C for HPLC-TEA and 900°C for GC/TEA was selected. As the authors pointed out, GC uses differences in vapour pressure and solubility in the liquid phase of the column to separate compounds, whereas in HPLC polarity, physical size and shape characteristics determine the chromatographic selectivity. So, the authors reported that the use of parallel HPLC-TEA and GC-TEA techniques provides a novel self-confirmatory capability, and because of the selectivity of the technique, there was no need for sample clean-up before analysis. The detector proved to be linear over six orders of magnitude. In the determination of explosives dissolved in acetone and diluted in methanol to obtain a 10-ppm (weight/volume) solution, the authors reported that no extraneous peaks were observed even when the samples were not previously cleaned up. Neither were they observed in the analysis of post-blast debris. Controlled experiments with handswabs spiked with known amounts of explosives indicated a lower detection limit of about 10 pg injected into column. 

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