Organic Explosives Research Articles

Mass spectrometry detection and imaging of inorganic and organic explosive device signatures using desorption electro-flow focusing ionization.

We demonstrate the coupling of desorption electro-flow focusing ionization (DEFFI) with in-source collision induced dissociation (CID) for the mass spectrometric (MS) detection and imaging of explosive device components, including both inorganic and organic explosives and energetic materials. We utilize in-source CID to enhance ion collisions with atmospheric gas, thereby reducing adducts and minimizing organic contaminants. Optimization of the MS signal response as a function of in-source CID potential demonstrated contrasting trends for the detection of inorganic and organic explosive device components. DEFFI-MS and in-source CID enabled isotopic and molecular speciation of inorganic components, providing further physicochemical information. The developed system facilitated the direct detection and chemical mapping of trace analytes collected with Nomex swabs and spatially resolved distributions within artificial fingerprints from forensic lift tape. The results presented here provide the forensic and security sectors a powerful tool for the detection, chemical imaging, and inorganic speciation of explosives device signatures.

Two Decades of Research on Nano‐Energetic Materials

Two Decades of Research on Nano‐Energetic Materials

Energetic lanthanide complexes: coordination chemistry and explosives applications

Metals are generally added to organic molecular explosives in a heterogeneous composite to improve overall heat and energy release. In order to avoid creating a mixture that can vary in homogeneity, energetic organic molecules can be directly bonded to high molecular weight metals, forming a single metal complex with Angstrom-scale separation between the metal and the explosive. To probe the relationship between the structural properties of metal complexes and explosive performance, a new series of energetic lanthanide complexes has been prepared using energetic ligands such as NTO (5-nitro-2,4-dihydro-1,2,4-triazole-3-one). These are the first examples of lanthanide NTO complexes where no water is coordinated to the metal, demonstrating novel control of the coordination environment. The complexes have been characterized by X-ray crystallography, NMR and IR spectroscopies, photoluminescence, and sensitivity testing. The structural and energetic properties are discussed in the context of enhanced blast effects and detection. Cheetah calculations have been performed to fine-tune physical properties, creating a systematic method for producing explosives with 'tailor made' characteristics. These new complexes will be benchmarks for further study in the field of metalized high explosives.

Decomposition of Condensed Phase Energetic Materials: Interplay between Uni- and Bimolecular Mechanisms

Activation energy for the decomposition of explosives is a crucial parameter of performance. The dramatic suppression of activation energy in condensed phase decomposition of nitroaromatic explosives has been an unresolved issue for over a decade. We rationalize the reduction in activation energy as a result of a mechanistic change from unimolecular decomposition in the gas phase to a series of radical bimolecular reactions in the condensed phase. This is in contrast to other classes of explosives, such as nitramines and nitrate esters, whose decomposition proceeds via unimolecular reactions both in the gas and in the condensed phase. The thermal decomposition of a model nitroaromatic explosive, 2,4,6-trinitrotoluene (TNT), is presented as a prime example. Electronic structure and reactive molecular dynamics (ReaxFF-lg) calculations enable to directly probe the condensed phase chemistry under extreme conditions of temperature and pressure, identifying the key bimolecular radical reactions responsible for the low activation route. This study elucidates the origin of the difference between the activation energies in the gas phase (~62 kcal/mol) and the condensed phase (~35 kcal/mol) of TNT and identifies the corresponding universal principle. On the basis of these findings, the different reactivities of nitro-based organic explosives are rationalized as an interplay between uni- and bimolecular processes.

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.

Analysis of Reaction Products of Lysozyme under the Explosion Condition by Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry

Identification and determination of explosives and explosive residues were a subject of continuing strong interest in analytical chemistry and forensic science. In this paper, the reaction products of lysozyme under the explosion condition were analyzed by a MALDI-TOFMS (Matrix-assisted laser desorption ionization time-of-flight mass spectrometry) method. There was no difference in the tryptic digest between the normal lysozyme and the reaction products generated by detonator, while some adduct peaks such as [MH+17]+, [MH+18]+, [MH+28]+, [MH+32]+, and [MH+44]+ were discovered in the explosives. This may be attributed to the reaction between the lysozyme and the active small molecule gases such as NH3, H2O, CO/N2, O2, CO2, which were generated during the explosion. Characteristic peaks which were produced by lysozyme and the active small molecule gases from different explosives can be used to discriminate the six explosives. For example, H2O molecules which were generated during the exploration by tri-nitrotoluene (TNT) can specifically react with VFGRCELAAAMKRHGLDNYR (m/z 2307) to produce a characteristic peak at m/z 2325 (2307+18). Also, H2O molecules which were generated by hexahydro-1,3,5-trinitroazine (RDX) can completely react with IVSDGNGMNAWVAWRNRCK (m/z 2177) to produce a characteristic peak at m/z (2177 + 18). Characteristic peak at m/z 1301 was produced by GYSLGNWVCAAK (m/z 1269) and O2 molecules for the identification of pentaerythritol tetranitrate (PETN). While for black powder, O2 and H2O can both react with IVSDGNGMNAWVAWR (m/z 1676) to produce product ions peaks at m/z 1694 and 1708. However, only the O2 molecules can react with IVSDGNGMNAWVAWR for pyrotechnic composition. As for ammon explosive, which is a mixture of inorganic explosives and organic explosives, CO2 molecules can react with a plurality of reaction sites of lysozyme to produce a series of characteristic peaks signals such as m/z 1313 (1269+44), 1720 (1676+44), 1848 (1804+44), 2722 (2678+44).

Primary and recombined emitting species in laser-induced plasmas of organic explosives in controlled atmospheres

The main difficulties in spectral interpretation of laser-induced plasmas from species containing C, N, O or H rely on the crossroad concerning their origin: direct release from native bonds of the molecule or recombination of atoms and molecular fragments with ambient constituents.

Maximum Compaction of Ionic Organic Explosives: Bis(hydroxylammonium) 5,5′‐Dinitromethyl‐3,3′‐bis(1,2,4‐oxadiazolate) and its Derivatives

Within this contribution on bis(oxadiazoles) we report on bis-hydroxylammonium 5,5'-dinitro-methyl-3,3'-bis(1,2,4-oxadiazolate), which (to the best of our knowledge) shows the highest density (2.00 g cm(-3) at 92 K, 1.95 g cm(-3) at RT) ever reported for an ionic CHNO explosive. Also the corresponding bis(ammonium) salt shows an outstanding density of 1.95 g cm(-3) (173 K). The reaction of the 3,3'-bis(1,2,4-oxadiazolyl)-5,5'-bis(2,2'-dinitro)-diacetic acid diethyl ester with different nitrogen-rich bases, such as ammonia, hydrazine, hydroxylamine, and triaminoguanidine causes decarboxylation followed by the formation of the corresponding salts (cation/anion stoichiometry 2:1). The reactions are performed at ambient temperature in H2O/MeOH mixtures and furnish qualitatively pure products showing characteristics of typical secondary explosives. The obtained compounds were characterized by multinuclear NMR spectroscopy, IR and Raman spectroscopy, as well as mass spectrometry. Single-crystal X-ray diffraction studies were performed and the structures of all compounds were determined at low temperatures. The thermal stability was measured by differential scanning calorimetry (DSC). The sensitivities were explored by using the BAM drophammer and friction test. The heats of formation were calculated by the atomization method based on CBS-4M enthalpies. With these values and the X-ray densities, several detonation parameters such as the detonation pressure, velocity, energy, and temperature were computed using the EXPLO5 code.

Advanced recognition of explosives in traces on polymer surfaces using LIBS and supervised learning classifiers

The large similarity existing in the spectral emissions collected from organic compounds by laser-induced breakdown spectroscopy (LIBS) is a limiting factor for the use of this technology in the real world. Specifically, among the most ambitious challenges of today's LIBS involves the recognition of an organic residue when neglected on the surface of an object of identical nature. Under these circumstances, the development of an efficient algorithm to disclose the minute differences within this highly complex spectral information is crucial for a realistic application of LIBS in countering explosive threats. An approach cemented on scatter plots of characteristic emission features has been developed to identify organic explosives when located on polymeric surfaces (teflon, nylon and polyethylene). By using selected spectral variables, the approach allows to design a concise classifier for alerting when one of four explosives (DNT, TNT, RDX and PETN) is present on the surface of the polymer. Ordinary products (butter, fuel oil, hand cream, olive oil and motor oil) cause no confusion in the decisions taken by the classifier. With rates of false negatives and false positives below 5%, results demonstrate that the classification algorithm enables to label residues according to their harmful nature in the most demanding scenario for a LIBS sensor.

Predicting Solubility of Military, Homemade, and Green Explosives in Pure and Saline Water using COSMO‐RS

AbstractThe conductor‐like screening model for real solvents (COSMO‐RS) has previously been shown to give accurate aqueous solubilities for a range of organic compounds using only quantum chemical simulation data. Application of this method for solid organic explosives, however, faces two difficulties; it requires correction for the free energy of fusion (a generally unknown quantity for these compounds) and it shows considerable error for common explosive classes such as nitramines. Herein we introduce a correction factor for COSMO‐RS that is applicable to a wide range of explosives, and requires no data beyond a quantum chemistry calculation. This modification allows COSMO‐RS to be used as a predictive tool for new proposed explosives or for systems lacking experimental data. We use this method to predict the temperature‐dependent solubility of solid explosives in pure and saline water to an average accuracy of approximately 0.25 log units at ambient temperature. Setschenow (salting‐out) coefficients predicted by this method show considerable improvement over previous COSMO‐RS results, but are still slightly overestimated compared to the limited experimental data available. We apply this method to a range of military, homemade, and “green” explosives that lack experimental seawater solubility data, an important property for environmental fate and transport modeling.

A fast liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) method for the identification of organic explosives and propellants

A fast, highly specific and sensitive method for the detection of an extensive list of organic explosives and propellants using an optimised Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry (LC-QToF-MS) procedure has been developed. Analyte specific information including retention time, adduct accurate mass and fragmentation data was firstly collected using both positive and negative ion Atmospheric Pressure Chemical Ionisation (APCI) and entered into a Personal Compound Database/Library (PCDL). The custom PCDL can then be used to screen any sample for the presence of organic explosives and propellants, generating a match score for any identified compounds. To date over 50 organic explosives and propellants have been characterised and entered into the database representing those likely to be encountered in forensic and environmental samples and also a range of specialist explosives.

Influence of Molecular Structure on the Laser-Induced Plasma Emission of the Explosive RDX and Organic Polymers

A series of organic polymers and the military explosive cyclotrimethylenetrinitramine (RDX) were studied using the light emission from a femtosecond laser-induced plasma under an argon atmosphere. The relationship between the molecular structure and plasma emission was established by using the percentages of the atomic species (C, H, N, O) and bond types (C-C, C═C, C-N, and C≡N) in combination with the atomic/molecular emission intensities and decay rates. In contrast to previous studies of organic explosives in which C2 was primarily formed by recombination, for the organic materials in this study the percentage of C-C (and C═C) bonds was strongly correlated to the molecular C2 emission. Time-resolved emission spectra were collected to determine the lifetimes of the atomic and molecular species in the plasma. Observed differences in decay rates were attributed to the differences in both the molecular structure of the organic polymers or RDX and the chemical reactions that occur within the plasma. These differences could potentially be exploited to improve the discrimination of explosive residues on organic substrates with laser-induced breakdown spectroscopy.

Gaseous byproducts from high‐temperature thermal conversion elemental analysis of nitrogen‐ and sulfur‐bearing compounds with considerations for δ2H and δ18O analyses

High-temperature, conversion-reduction (HTC) systems convert hydrogen and oxygen in materials into H2 and CO for δ(2)H and δ(18)O measurements by isotope ratio mass spectrometry. HTC of nitrogen- and sulfur-bearing materials produces unintended byproduct gases that could affect isotope analyses by: (1) allowing isotope exchange reactions downstream of the HTC reactor, (2) creating isobaric or co-elution interferences, and (3) causing deterioration of the chromatography. This study characterizes these HTC byproducts. A HTC system (ThermoFinnigan TC/EA) was directly connected to a gas chromatograph/quadrupole mass spectrometer in scan mode (m/z 8 to 88) to identify the volatile products generated by HTC at conversion temperatures of 1350 °C and 1450 °C for a range of nitrogen- and sulfur-bearing solids [keratin powder, horse hair, caffeine, ammonium nitrate, potassium nitrate, ammonium sulfate, urea, and three nitrated organic explosives (PETN, RDX, and TNT)]. The prominent HTC byproduct gases include carbon dioxide, hydrogen cyanide, methane, acetylene, and water for all nitrogen-bearing compounds, as well as carbon disulfide, carbonyl sulfide, and hydrogen sulfide for sulfur-bearing compounds. The 1450 °C reactor temperature reduced the abundance of most byproduct gases, but increased the significant byproduct, hydrogen cyanide. Inclusion of a post-reactor chemical trap containing Ascarite II and Sicapent, in series, eliminated the majority of byproducts. This study identified numerous gaseous HTC byproducts. The potential adverse effects of these gases on isotope ratio analyses are unknown but may be mitigated by higher HTC reactor temperatures and purifying the products with a purge-and-trap system or with chemical traps.

An investigation into the fate of organic explosives in soil

Soil samples collected from directly beneath the point of detonation of an Improvised Explosive Device (IED) are recognized as a potential source of explosive residues. In this study, 17 organic explosives were spiked into three different soil types and stored at room temperature for 56 days. Periodic solvent extraction and quantification using liquid chromatography-ultraviolet detection (LC-UV) was used to determine the impact of prolonged storage on analyte concentration. Results indicate that tetryl, trinitrobenzene, and trinitrotoluene undergo rapid transformation within four hours of storage in soil samples, leading to their non-detection in less than two weeks. Transformation rates of the dinitro-aromatics and nitrate esters were dependent upon soil composition with significantly reduced analyte concentrations detected after 56 days, while nitramines underwent limited transformation. A reduction in soil storage temperature to 4°C was successful only in reducing the rate of analyte transformation for the dinitro-aromatics and nitrate esters, with soil freezing required to arrest analyte transformation.

Stability of explosive residues in methanol/water extracts, on alcohol wipes and on a glass surface

The stability of four target organic explosives [pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and triacetone triperoxide (TATP)] and two inorganic anions (chlorate and nitrate) on polyester-based alcohol wipes and in 60% (v/v) methanol/water extracts, stored over 30 days in clear and amber glass vials at three different temperatures, was investigated in order to establish storage recommendations. The retention of all six representative compounds on a glass surface at two different storage temperatures was also included as a preliminary study on the stability of explosive residues on stored exhibits (such as post-blast debris).The results from the stability study suggested that, after sampling, the wipes should be stored in a dark and low temperature environment. Also, after extracting the wipes with 60% (v/v) methanol/water (as in our previously reported recommended protocol), the extracts should be stored in a similar fashion.The results from the retention study on the glass substrate suggested that exhibits should be stored at the lowest temperature possible to minimise the loss of TNT or TATP (or similar target compounds) that might be present as residues.

Comparison of post-detonation combustion in explosives incorporating aluminum nanoparticles: Influence of the passivation layer

Aluminum nanoparticles and explosive formulations that incorporate them have been a subject of ongoing interest due to the potential of aluminum particles to dramatically increase energy content relative to conventional organic explosives. We have used time-resolved atomic and molecular emission spectroscopy to monitor the combustion of aluminum nanoparticles within the overall chemical dynamics of post-detonation fireballs. We have studied the energy release dynamics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges incorporating three types of aluminum nanoparticles: commercial oxide-passivated nanoparticles, oleic acid-capped aluminum nanoparticles (AlOA), and nanoparticles in which the oxide shell of the particle has been functionalized with an acrylic monomer and copolymerized into a fluorinated acrylic matrix (AlFA). The results indicate that the commercial nanoparticles and the AlFA nanoparticles are oxidized at a similar rate, while the AlOA nanoparticles combust more quickly. This is most likely due to the fact that the commercial nano-Al and the AlFA particles are both oxide-passivated, while the AlOA particles are protected by an organic shell that is more easily compromised than an oxide layer. The peak fireball temperatures for RDX charges containing 20 wt. % of commercial nano-Al, AlFA, or AlOA were ∼3900 K, ∼3400 K, and ∼4500 K, respectively.

A portable explosive detector based on fluorescence quenching of pyrene deposited on coloured wax-printed μPADs

A new technique for the detection of explosives has been developed based on fluorescence quenching of pyrene on paper-based analytical devices (μPADs). Wax barriers were generated (150 °C, 5 min) using ten different colours. Magenta was found as the most suitable wax colour for the generation of the hydrophobic barriers with a nominal width of 120 μm resulting in fully functioning hydrophobic barriers. One microliter of 0.5 mg mL(-1) pyrene dissolved in an 80:20 methanol-water solution was deposited on the hydrophobic circle (5 mm diameter) to produce the active microchip device. Under ultra-violet (UV) illumination, ten different organic explosives were detected using the μPAD, with limits of detection ranging from 100-600 ppm. A prototype of a portable battery operated instrument using a 3 W power UV light-emitting-diode (LED) (365 nm) and a photodiode sensor was also built and evaluated for the successful automatic detection of explosives and potential application for field-based screening.

Non-contact halogen lamp heating assisted LTP ionization miniature rectilinear ion trap: a platform for rapid, on-site explosives analysis

A platform consisting of a halogen lamp, a low temperature plasma (LTP) probe, and a miniature rectilinear ion trap mass spectrometer (RIT-MS) has been constructed and evaluated to detect organic and inorganic explosives on solid surfaces. This platform features two attractive characteristics: high sensitivity for the explosives with low volatility, and rapid analysis speed for the explosives on large surface areas. With non-contact heating by the halogen lamp, the signal intensities for the explosives with relatively high volatility were improved by over an order of magnitude, compared to those obtained at room temperature; and even more, the explosives with low volatility, which could hardly be detected at room temperature, were able to be readily identified. The limits of detection (LODs) of the selected explosives were all at the picogram level (e.g., 10 pg and 20 pg for TNT and RDX, respectively) with a heating time of 3 s. Using manual surface swabbing, the analysis of explosives on a large surface area (7.5 cm × 2.5 cm) was accomplished within 10 s, and an acceptable sensitivity could be acquired; additionally, inorganic explosives (black powder and firecracker) were successfully detected. Without any sample pretreatment, the platform was used to analyze the wastewater from an explosives factory, confirming the existence of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,6-dinitrotoluene (2,6-DNT), and the concentration of TNT was determined to be 5 ngmL(-1). All these results indicated that the proposed platform was a promising technique for security monitoring and environmental analysis.

A Comparison of Solvent Extract Cleanup Procedures in the Analysis of Organic Explosives

The use of an organic solvent to extract explosive residues from hand swabs and postblast debris inevitably leads to the coextraction of unwanted materials, usually in far greater quantities than any explosive residue. In this study, the extraction efficiency of a number of solvent cleanup procedures including solid-phase extraction (SPE), adsorbent resins such as Chromosorb-104, and traditional materials such as silica and Florisil was calculated using a quantitative liquid chromatography-ultraviolet (LC-UV) detection procedure. The Oasis(®) HLB cartridge outperformed other cleanup procedures, with analyte recoveries approaching 95%, while the Amberlite XAD-7 procedure returned the lowest overall recoveries. The matrix rejection ability of each method was then determined using a simulated highly contaminated matrix, with the adsorbent resins showing a higher degree of matrix rejection, which is seen as a reduction in background noise in the UV chromatogram using 210nm detection.

Detection of explosives with laser-induced breakdown spectroscopy

Our recent work on the detection of explosives by laser-induced breakdown spectroscopy (LIBS) is reviewed in this paper. We have studied the physical mechanism of laser-induced plasma of an organic explosive, TNT. The LIBS spectra of TNT under single-photon excitation are simulated using MATLAB. The variations of the atomic emission lines intensities of carbon, hydrogen, oxygen, and nitrogen versus the plasma temperature are simulated too. We also investigate the time-resolved LIBS spectra of a common inorganic explosive, black powder, in two kinds of surrounding atmospheres, air and argon, and find that the maximum value of the O atomic emission line SBR of black powder occurs at a gate delay of 596 ns. Another focus of our work is on using chemometic methods such as principle component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) to distinguish the organic explosives from organic materials such as plastics. A PLS-DA model for classification is built. TNT and seven types of plastics are chosen as samples to test the model. The experimental results demonstrate that LIBS coupled with the chemometric techniques has the capacity to discriminate organic explosive from plastics.