Identification of Inorganic Improvised Explosive Devices by Analysis of Postblast Residues Using Portable Capillary Electrophoresis Instrumentation and Indirect Photometric Detection with a Light-Emitting Diode

Abstract

A commercial portable capillary electrophoresis (CE) instrument has been used to separate inorganic anions and cations found in postblast residues from improvised explosive devices (IEDs) of the type used frequently in terrorism attacks. The purpose of this analysis was to identify the type of explosive used. The CE instrument was modified for use with an in-house miniaturized lightemitting diode (LED) detector to enable sensitive indirect photometric detection to be employed for the detection of 15 anions (acetate, benzoate, carbonate, chlorate, chloride, chlorite, cyanate, fluoride, nitrate, nitrite, perchlorate, phosphate, sulfate, thiocyanate, thiosulfate) and 12 cations (ammonium, monomethylammonium, ethylammonium, potassium, sodium, barium, strontium, magnesium, manganese, calcium, zinc, lead) as the target analytes. These ions are known to be present in postblast residues from inorganic IEDs constructed from ammonium nitrate/fuel oil mixtures, black powder, and chlorate/perchlorate/sugar mixtures. For the analysis of cations, a blue LED (470 nm) was used in conjunction with the highly absorbing cationic dye, chrysoidine (absorption maximum at 453 nm). A nonaqueous background electrolyte comprising 10 mM chrysoidine in methanol was found to give greatly improved baseline stability in comparison to aqueous electrolytes due to the increased solubility of chrysoidine and its decreased adsorption onto the capillary wall. Glacial acetic acid (0.7% v/v) was added to ensure chrysoidine was protonated and to enhance separation selectivity by means of complexation with transition metal ions. The 12 target cations were separated in less than 9.5 min with detection limits of 0.11-2.30 mg/L (calculated at a signal-to-noise ratio of 3). The anions separation system utilized a UV LED (370 nm) in conjunction with an aqueous chromate electrolyte (absorption maximum at 371 nm) consisting of 10 mM chromium(VI) oxide and 10 mM sodium chromate, buffered with 40 mM tris(hydroxymethyl)-aminomethane at pH 8.05. All 15 target anions were baseline separated in less than 9 min with limits of detection ranging from 0.24 to 1.15 mg/L (calculated at a signal-to-noise ratio of 3). Use of the portable instrumentation in the field was demonstrated by analyzing postblast residues in a mobile laboratory immediately after detonation of the explosive devices. Profiling the ionic composition of the inorganic IEDs allowed identification of the chemicals used in their construction.Improvised explosive devices (IEDs) constructed by terrorists often contain "homemade" explosives rather than high explosives, such as nitrated organic compounds (e.g., 2,4,6-trinitrotoluene, TNT), because of the relative ease with which the components used in their manufacture can be procured. Typically, IEDs comprise an explosive created from unrestricted materials and an initiation system involving an electrical charge and a detonator. Inorganic homemade explosives employ vigorous oxidation/ reduction chemical reactions using strong inorganic oxidizers such as nitr...

Identification of inorganic ions in post‐blast explosive residues using portable CE instrumentation and capacitively coupled contactless conductivity detection

“…Inorganic ions are highly prevalent and measurement of their levels is important in a wide variety of sample matrices, including environmental [1][2][3][4][5], foods [6], industrial [7,8] and forensic samples [9][10][11]. Determination of these species can be performed by wet chemical methods [12], gravimetry [13], potentiometry [14], flow-injection analysis [15], atomic spectroscopy [16,17], ion chromatography [2] and electrophoretic methods in capillary [5,18,19] and microchip [20] formats.…”

“…Previous work in our laboratory [11] has used a commercial portable CE instrument modified to include a LED indirect photometric detector for the universal detection of inorganic anions and cations in post-blast residues from homemade explosives. The present study extends the previous work by introducing novel methods for the separation of a large range of inorganic anions and cations using a C 4 D. C 4 D detection is shown to be significantly more sensitive than indirect photometric detection, and the new separations are considerably faster and use less hazardous electrolytes than the methods reported previously.…”

Portable capillary-based (non-chip) capillary electrophoresis

“…3). The system is enclosed in a compact attaché case and connected to a laptop [56][57][58][59][60][61][62][63]. Li et al presented the first version in 2001 for environmental applications [63].…”

“…A second version of the system extended the detection options and the PGD provided [58,61,63] with the possibility of connection to other different types of detector {e.g., spectrophotometric UV-Vis [57,60], contactless conductivity [56,59], or a custom-built photometric detector using light emitting diodes (LEDs) [62]} . Even though the option of the several external detectors brought versatility in detection modes, a significant increase in weight to 10 kg was reported.…”

“…The benefit of the broad range of available detectors allowed new applications to be developed for this P-CE, e.g. : determination of low-molecular-weight organic acids in the presence of chlorinated herbicides [59]; determination of toxic pyrrolizidine alkaloids in traditional Chinese medicine [60]; and, analysis of post-blast residues for identification of inorganic improvised explosive devices [62]. Even though the weight of the newest upgraded model of the P-CE was double that of the first model, it remains a commercial portable P-CE.…”