Fingerprinting postblast explosive residues by portable capillary electrophoresis with contactless conductivity detection

A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of postblast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual‐opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from postblast residues using an optimized separation electrolyte composed of 20 mM MES, 20 mM l ‐histidine, 30 μM CTAB and 2 mM 18‐crown‐6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive.     

On-Line SPE Coupled with LC�CAPCI�CMS for the Determination of Trace Explosives in Water

In this study, a rapid, sensitive, and fully automated on-line solid phase extraction (SPE)?Cliquid chromatography (LC)?Cmass spectrometry (MS) method for the analysis of explosive residues in water, was systematically investigated. First, separation of explosive residues was achieved by reverse-phase chromatography using an XDB-C18 column in 30 min with an eluent containing 0.1% acetic acid, 5 mM ammonium acetate, and methanol. Secondly, atmospheric pressures chemical ionization (APCI) and electrospray ionization (ESI) interfaced with the MS detector were used to examine the explosive residues, indicating that APCI?CMS was more suitable than ESI?CMS for the detection of explosives. Thirdly, the conditions for on-line SPE, including solvent pH and sample injected volume, were optimized. The calibration curves obtained for all explosives studied were linear in the concentration range 0.5?C50 ??g L^?1. The detection limits of this method ranged from 0.05 to 0.5 ??g L^?1 when 4000 ??L of sample was on-line pre-concentrated on C18 enrichment column. The recoveries from lake waters spiked with explosive standard solution ranged from 90.5 to 108.0%. The proposed method is simple, fast, and could be applied successfully to the analysis of explosive residues in contaminated water without any further pretreatment.     

Synthesis and characterization of 1‐methyl‐2,4,5‐trinitroimidazole (MTNI)

We have reinvestigated the synthesis of 1‐methyl‐2,4,5‐trinitroimidazole (MTNI; 1 ), and further characterized its physical properties. It is a promising candidate as an insensitive high explosive. Compound 1 was synthesized from the imidazole ( 2 ), via a 5‐step sequence of reactions, and subjected to various sensitivity tests for explosives. The structure of 1 was characterized by X‐ray diffraction. The crystal is orthorhombic; C₄H₃N₅O₆, M = 217.11, Z = 8, Pca2₁, a = 8.6183(6) Å, b = 17.7119(12) Å, c = 10.6873(7) Å, V = 1631.38(19) ų, Dc = 1.768 g/cm³. The structure was refined to R = 0.0284 for 3201 independent reflections with I > 2σ(I). The molecular structures calculated by high levels of ab initio and density functional theories were in good agreement with those observed by X‐ray experiment. According to our preliminary sensitivity tests, 1 was characterized to be intermediate in sensitivity between RDX and TNT. The explosive performances were evaluated theoretically, and were found to be comparable to those of RDX. In addition, owing to its low melting point (82 °C), 1 is believed to be an excellent candidate for inclusion in melt‐castable explosives, and may lead to increased explosive power.     

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

2,3‐Dimethyl‐2,3‐dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour‐phase detection systems. In this study, the formation and detection of gas‐phase [M+H]⁺, [M+Li]⁺, [M+NH₄]⁺ and [M+Na]⁺ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]⁺ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]⁺ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision‐induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source‐formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]⁺ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.     

Solid-phase microextraction coupled to gas chromatography for the determination of 2,3-dimethyl-2,3-dinitrobutane as a marking agent for explosives

This paper investigates the detection of 2,3-dimethyl-2,3-dinitrobutane (DMNB), a marking agent in explosives, by gas chromatography (GC) with electron capture detection using solid-phase microextraction (SPME) as a sample preparation technique. The 25,27-dihydroxy-26,28-oxy (2′,7′-dioxo-3′,6′-diazaoctyl) oxy-p-tert-butylcalix[4]arene/hydroxy-terminated silicone oil coated fiber was highly sensitive to trap DMNB from ammonium nitrate matrix. The analysis was performed by extracting 2 g of explosives for 30 s at room temperature and then immediately introducing into the heated GC injector for 1 min of thermal desorption. The method showed good linearity in the range from 0.01 to 1.0 μg/g. The relative standard deviations for these extractions were <8%. The calculated limit of detection for DMNB (S/N = 3) was 4.43 × 10⁻⁴ μg/g, which illustrates that the proposed systems are suitable for explosive detection at trace level. This is the first report of an SPME-GC system shown to extract marking agent in explosives for subsequent detection in a simple, rapid, sensitive, and inexpensive manner.     

Identification of dominant odor chemicals emanating from explosives for use in developing optimal training aid combinations and mimics for canine detection

Despite the recent surge in the publication of novel instrumental sensors for explosives detection, canines are still widely regarded as one of the most effective real-time field method of explosives detection. In the work presented, headspace analysis is performed by solid phase microextraction (SPME)/gas chromatography-mass spectrometry (GC-MS), and gas chromatography-electron capture detection (GC-ECD), and used to identify dominant explosive odor chemicals seen at room temperature. The activity of the odor chemicals detected was determined through field trials using certified law enforcement explosives detection canines. A chemical is considered an active explosive odor when a trained and certified explosives detection canine alerts to a sample containing that target chemical (with the required controls in place). A sample to which the canine does not alert may be considered an inactive odor, but it should be noted that an inactive odor might still have the potential to enhance an active odor's effect. The results presented indicate that TNT and cast explosives share a common odor signature, and the same may be said for plasticized explosives such as Composition 4 (C-4) and Detasheet. Conversely, smokeless powders may be demonstrated not to share common odors. The implications of these results on the optimal selection of canine training aids are discussed.     

Fe‐enriched Clay‐coated and Reduced Graphene Oxide‐modified N‐doped Polymer Nanocomposite: A Natural Recognition Element‐based Sensing Electrode for DNT

Dinitrotoluene (DNT) is a signature material of all nitro‐aromatic explosives including the lethal 2,4,6‐trinitrotoluene (TNT). A clay‐modified reduced graphene oxide (rGO)‐polymer nanocomposite was prepared as sensing electrode for the detection of (DNT) in the aquatic systems. rGO was in situ dispersed in the electro‐conductive N‐doped phenol/formaldehyde polymer and the clay ‘montmorillonite’ was coated on the nanocomposite. The clay, containing iron as one of its mineral components, served as the recognition element for DNT. Tested using electrochemical measurement techniques – cyclic voltammetry and differential pulse voltammetry, the prepared sensing electrode exhibited a low detection limit (0.0016 μM) on signal to noise ratio basis (S/N=3) and excellent linearity (R²=0.997) over 0.02–10 mg L^?1 with high sensitivity value (428 μA mM^?1 cm^?2) for DNT. The electrode showed negligible interference with the gravimetric and volumetric salts commonly present in seawater, and also, with explosive derivatives. The separate tests performed in a simulated seawater confirmed the suitability of the prepared electrode for use in field applications.     

Rapid,on-site identification of explosives in nanoliter droplets using a UV reflected fiber optic sensor

A portable UV (190–400 nm) spectrophotometric based reflected fiber optic sensor system is presented for the on-site detection and identification of explosives. A reflected fiber optic sensor for explosives analysis was developed, with low sample consumption (20–100 nL) and a wide concentration quantification range (1.1–250 mg L⁻¹). Seven common explosives [pentaerythritol tetranitrate (PETN), trinitrophenylmethylnitramine (CE), trinitrotoluene (TNT), dinitrotoluene (DNT), picric acid (PA), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX)] and a PETN–RDX mixture (to simulate the Semtex used in many terrorist bombings) were quantitatively analyzed and identified by the proposed system in less than 3 s per test, with limits of detection (LOD) of 0.3 mg L⁻¹. Due to chemical interference problems in the UV wavelengths range, a novel feature matching algorithm (FMA) was proposed for explosive identification, which was proved to have higher specificity and better anti-interference ability. Real post-blast debris samples were analyzed by the proposed method, and the results were validated against an LC/MS/MS method. The rapid, cost-effective detection with low sample consumption and wide applicability achieved by this system is highly suitable for homeland security on-site applications, such as rapid sample screening in post-blast debris.     

Vibrational spectroscopy standoff detection of explosives

Standoff infrared and Raman spectroscopy (SIRS and SRS) detection systems were designed from commercial instrumentation and successfully tested in remote detection of high explosives (HE). The SIRS system was configured by coupling a Fourier-transform infrared interferometer to a gold mirror and detector. The SRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HE samples were detected on stainless steel surfaces as thin films (2–30 μg/cm²) for SIRS experiments and as particles (3–85 mg) for SRS measurements. Nitroaromatic HEs: TNT, DNT, RDX, C4, and Semtex-H and TATP cyclic peroxide homemade explosive were used as targets. For the SIRS experiments, samples were placed at increasing distances and an infrared beam was reflected from the stainless steel surfaces coated with the target chemicals at an angle of ∼180° from surface normal. Stainless steel plates containing TNT and RDX were first characterized for coverage distribution and surface concentration by reflection–absorption infrared spectroscopy. Targets were then placed at the standoff distance and SIRS spectra were collected in active reflectance mode. Limits of detection (LOD) were determined for all distances measured for the target HE. LOD values of 18 and 20 μg/cm² were obtained for TNT and RDX, respectively, for the SIR longest standoff distance measured. For SRS experiments, as low as 3 mg of TNT and RDX were detected at 7 m source–target distance employing 488 and 514.5 nm excitation wavelengths. The first detection and quantification study of the important formulation C4 is reported. Detection limits as function of laser powers and acquisition times and at a standoff distance of 7 m were obtained.     

A Simple Method for Reliable Estimation of the Bubble Energy in the Underwater Explosion

The bubble energy is the main part of the chemical energy of the explosive that is formed upon the propagation of a shock wave through the water for the underwater explosion. A simple method is introduced for reliable prediction of the bubble energy of composite explosives containing aluminum (Al) and/or ammonium perchlorate (AP). It is shown that the bubble energy of composite Al/AP explosives depends on the number of moles of chlorine, carbon, and Al atoms. Experimental data of 56 composite Al/AP explosives are used to construct and test the novel model of the bubble energy. Statistical parameters of the new model, in external validation containing 35 composite Al/AP explosives as the training set, have the values 0.43 and 1.15 MJ · kg^–1 for the root mean squared error (RMSE) and maximum of errors (Max Error) of the new model, respectively. The values of RMSE and Max Error for 21 composite Al/AP explosives as test set are also 0.60 and 2.22 MJ · kg^–1, respectively. Cross validations of the new method corresponding to the coefficients of determination for leave‐one‐out (Q²_LOO) and the fivefold cross validation (Q²_5CV) are 0.8573 and 0.8403, respectively, which confirms goodness‐of‐fit, goodness‐of‐prediction, accuracy and precision of the novel model. It is shown that the novel correlation can be applied for pure and composite explosives, which do not contain Al/AP.     

Potassium 4,4′‐Bis(dinitromethyl)‐3,3′‐azofurazanate: A Highly Energetic 3D Metal–Organic Framework as a Promising Primary Explosive

Environmentally acceptable alternatives to toxic lead‐based primary explosives are becoming increasingly important for energetic materials. In this study, potassium 4,4′‐bis(dinitromethyl)‐3,3′‐azofurazanate, comprising two dinitromethyl groups and an azofurazan moiety, was synthesized and isolated as a new energetic 3D metal–organic framework (MOF). Several attractive properties, including a density of 2.039 g cm^?3, a decomposition temperature of 229 °C, a detonation velocity of 8138 m s^?1, a detonation pressure of 30.1 GPa, an impact sensitivity of 2 J, and friction sensitivity of 20 N make 4 a good candidate as a green primary explosive.     

Construction and Evaluation of a Fluorescent Sensor for the Detection of High Explosives

A sensor for the detection of airborne nitrate explosives was developed and laboratory tested. The device consisted of a quartz optical fiber, of which a 4-cm length was stripped and treated with an aminoalkylmethoxysilane. A fluorescent surface was produced by chemically attaching a sulfonated polyaromatic fluorophore to the amino group of the silylated quartz. Excitation was effected by radiation admitted through the fiber. When explosive laden air was drawn across the fluorescent surface, the analyte molecules interacted with the fluorophore and caused the emission to be quenched. This signal was monitored as an indicator of the explosive and was shown to be effective for TNT, di- and mononitrotoluenes, Tetryl, RDX, and HMX (marginal). Sensitivities were in the ng/m³range, and the surface could be flushed and restored after a quenching episode. Few interferences were encountered among common substances brought in contact with the surface.     

Rapid separation of post‐blast explosive residues on glass electrophoresis microchips

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C⁴D) for the separation and detection of inorganic anions in post‐blast explosive residues. The best separation condition was achieved using a running buffer composed of 35 mmol/L lactic acid, 10 mmol/L histidine and 0.070 mmol/L cetyl(trimethyl ammonium) bromide. For C⁴D measurements, the highest sensitivity was obtained applying a 700 kHz sinusoidal wave with excitation voltage of 20 V_pp. The separation of Cl^?, NO₃^?, NO₂^?, SO₄^2?, ClO₄^? and ClO₃^? was performed within ca. 150 s with baseline resolution and efficiencies between 4.4 × 10⁴ and 1.7 × 10⁵ plates/m. The found limits of detection ranged between 2.5 and 9.5 μmol/L. Last, real samples of post‐blast explosive residues were analyzed on the ME‐C⁴D devices obtaining successfully the determination of Cl^?, NO₃^? and SO₄^2?. The achieved concentration values varied between 12.8–72.5 mg/L for Cl^?, 1.7–293.1 mg/L for NO₃^? and 1.3–201.3 mg/L for SO₄^2?. The data obtained using ME‐C⁴D devices were in good agreement with the concentrations found by ion chromatography. The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the ME‐C⁴D devices emerge as a powerful and portable analytical platform for on‐site analysis demonstrating to be a promising tool for the crime scene investigation.     

A Simple Correlation for Assessment of the Shock Wave Energy in Underwater Detonation

Assessment of underwater detonation (explosion) is important for industrial purposes such as blasting cut of old warship, blasting droll and decoupled charge of blast underwater. Calculation of the shock wave energy requires several expensive experimental data such as the shock wave pressure and the representative time of the process. This work introduces a simple method for reliable prediction of the shock wave energy of composite explosives containing aluminum (Al) and/or ammonium perchlorate (AP), which show non‐ideal behavior. This method is based on the composition, loading density and the ratio of R/m^1/3, where R is the distance between the pressure gauge and charge as well as m is the mass of explosive charge. The measured data for 86 and 21 composite Al/AP explosives are used to construct and test the new model. Statistical parameters including the root mean squared error (RMSE), and maximum of errors (Max Error) of the new model are 0.11 and 0.39 MJ · kg^–1, respectively, which confirm high reliability of the new method. The values of RMSE and Max Error for test set are 0.13 and 0.30 MJ · kg^–1, respectively. Cross validation of the novel model is also used to evaluate its goodness‐of‐fit, goodness‐of‐prediction, accuracy and precision. It is shown that the novel correlation can be applied for pure and composite explosives without Al/AP.     

Analysis of explosives using differential mobility spectrometry

Characterization of ions from eight explosives (2,4,6-trinitrotoluene, pentaerythritol tetranitrate, 2,4,6-trinitrophenol, 2,4-dinitrotoluene, erythritol tetranitrate, hexamethylene triperoxide diamine, 2,4,6-trinitrophenylmethylnitramine and 1,3,5-trinitro-perhydro-1,3,5-triazine) using differential mobility spectrometry (DMS) with ⁶³Ni as an ionization source was performed. Presented results of explosive analysis have been evaluated by use of special software tool which communicates with DMS in real time. This tool was developed for visualization, identification and comparison of measured data. Each explosive provides characteristic signal at a specific compensation voltage under a fixed dispersion field. Peaks in DMS spectra for these ions were confined to a range of compensation voltages between ?1.61 to +1.71 V at RF = 1060 V. We calculated specific alpha coefficients (α₂ and α₄) to obtain a nonlinear function of explosives, based on their DMS spectra. Dependence of mobility for measured explosives ions in electric field at E/N values between 0 to 120 Td were used to inspectional graphical differentiation of explosives.     

Gas chromatographic detection of some nitro explosive compounds in soil samples after solid‐phase microextraction with carbon ceramic copper nanoparticle fibers

In this research, a new solid‐phase microextraction fiber based on carbon ceramic composites with copper nanoparticles followed by gas chromatography with flame ionization detection was applied for the extraction and determination of some nitro explosive compounds in soil samples. The proposed method provides an overview of trends related to synthesis of solid‐phase microextraction sorbents and their applications in preconcentration and determination of nitro explosives. The sorbents were prepared by mixing of copper nanoparticles with a ceramic composite produced by mixture of methyltrimethoxysilane, graphite, methanol, and hydrochloric acid. The prepared sorbents were coated on copper wires by dip‐coating method. The prepared nanocomposites were evaluated statistically and provided better limits of detection than the pure carbon ceramic. The limit of detection of the proposed method was 0.6 μg/g with a linear response over the concentration range of 2–160 μg/g and square of correlation coefficient >0.992. The new proposed fiber has been demonstrated to be a suitable, inexpensive, and sensitive candidate for extraction of nitro explosive compounds in contaminated soil samples. The constructed fiber can be used more than 100 times without the need for surface generation.     

High-throughput walkthrough detection portal for counter terrorism: detection of triacetone triperoxide (TATP) vapor by atmospheric-pressure chemical ionization ion trap mass spectrometry

With the aim of improving security, a high‐throughput portal system for detecting triacetone triperoxide (TATP) vapor emitted from passengers and luggage was developed. The portal system consists of a push‐pull air sampler, an atmospheric‐pressure chemical ionization (APCI) ion source, and an explosives detector based on mass spectrometry. To improve the sensitivity of the explosives detector, a novel linear ion trap mass spectrometer with wire electrodes (wire‐LIT) is installed in the portal system. TATP signals were clearly obtained 2 s after the subject under detection passed through the portal system. Preliminary results on sensitivity and throughput show that the portal system is a useful tool for preventing the use of TATP‐based improvised explosive devices by screening persons in places where many people are coming and going. Copyright © 2011 John Wiley & Sons, Ltd.     

Micellar electrokinetic chromatography and capillary electrochromatography of nitroaromatic explosives in seawater

The ability to separate nitroaromatic and nitramine explosives in seawater sample matrices is demonstrated using both MEKC and CEC. While several capillary-based separations exist for explosives, none address direct sampling from seawater, a sample matrix of particular interest in the detection of undersea mines. Direct comparisons are made between MEKC and CEC in terms of sensitivity and separation efficiency for the analysis of 14 explosives and explosive degradation products in seawater and diluted seawater. The use of high-salt stacking with MEKC results, on average, in a three-fold increase in the number of theoretical plates, and nearly double resolution for samples prepared in 25% seawater. By taking advantage of long injection times in conjunction with stacking, detection limits down to sub mg/L levels are attainable; however, resolution is sacrificed. CEC of explosive mixtures using sol-gels prepared from methyltrimethoxysilane does not perform as well as MEKC in terms of resolving power, but does permit extended injection times for concentrating analyte onto the head of the separation column with little or no subsequent loss in resolution. Electrokinetic injections of 8 min at high voltage allow for detection limits of explosives below 100 microg/L.     

Analysis of ascorbic acid based black powder substitutes by high‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry

Black powder substitutes are an important sub‐group of explosive propellants in the United States because they are readily accessible, and can be used as fillers for improvised explosive devices. Many brands of black powder substitutes incorporate an ascorbic acid fuel source with potassium nitrate (KNO₃) and/or potassium perchlorate (KClO₄) oxidizer(s). A gradient high‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry (HPLC/ESI‐QToFMS) method has been developed for the analysis of both the organic and the inorganic constituents. The HPLC/ESI‐QToFMS method was utilized to examine aqueous extracts of intact samples and post‐burn residues from six different brands of ascorbic acid based powders. Aqueous extracts of the post‐blast residues from two brands of ascorbic acid based propellant were also analyzed. The results showed that both the ascorbic acid fuel and the inorganic oxidizer(s) KClO₄ and/or KNO₃ were successfully detected via the [M–H]^? ion of ascorbic acid and the anions (ClO and NO) of the oxidizers. This method was proven to be a rapid and efficient procedure for the analysis of this class of explosives. The high mass resolution provided by the QToFMS instrument fulfills the degree of certainty required in a court of law. Published in 2010 by John Wiley & Sons, Ltd.     

The Application of Analytical Methods to the Detection of Hidden Explosives and Explosive Devices

The detection of hidden explosives has undergone an enormous development due to an increased desire for safety and the increased terrorist attacks in the last few years. This development was made possible in particular by the rapid advances in the development of powerful analytical techniques in general. These technologies, however, must be specially adapted for the problems of explosives detection. These problems encompass, for example, the large variety of different explosives, the camouflage of explosive devices, and the complexity of the composition of suspicious objects. Frequent air-travelers have most certainly already been confronted with a so-called explosives detection apparatus. Baggage controls at airports are a very important and well-known example of the application of detection technologies. This example also serves to demonstrate the high technological requirements, such as the variability of the object to be examined and a control procedure for a sealed object that must be completed with high reliability in a short period of time. The search for explosive devices or weapons cannot, however, be limited to the recognition of an external appearance with the help of X-ray imaging. These days, explosive devices, in particular, can readily be installed and hidden in objects of daily life by the use of tiny electric and electronic elements. Therefore, in addition to the application of X-ray imaging, the use of other technologies becomes necessary. The following article describes and discusses methods and scientific limits of explosives detection under the precondition of possible use at security checkpoints. For corrigendum see DOI: 10.1002/anie.199713711