Explosive Samples Research Articles

Combined use of direct analysis in real-time/Orbitrap mass spectrometry and micro-Raman spectroscopy for the comprehensive characterization of real explosive samples.

Direct Analysis in Real Time (DART™) high-resolution Orbitrap™ mass spectrometry (HRMS) in combination with Raman microscopy was used for the detailed molecular level characterization of explosives including not only the charge but also the complex matrix of binders, plasticizers, polymers, and other possible organic additives. A total of 15 defused military weapons including grenades, mines, rockets, submunitions, and mortars were examined. Swabs and wipes were used to collect trace (residual) amounts of explosives and their organic constituents from the defused military weapons and micrometer-size explosive particles were transferred using a vacuum suction-impact collection device (vacuum impactor) from wipe and swap samples to an impaction plate made of carbon. The particles deposited on the carbon plate were then characterized using micro-Raman spectroscopy followed by DART-HRMS providing fingerprint signatures of orthogonal nature. The optical microscope of the micro-Raman spectrometer was first used to localize and characterize the explosive charge on the impaction plate which was then targeted for identification by DART-HRMS analysis in both the negative and positive modes. Raman spectra of the explosives TNT, RDX and PETN were acquired from micrometer size particles and characterized by the presence of their characteristic Raman bands obtained directly at the surface of the impaction plate nondestructively without further sample preparation. Negative mode DART-HRMS confirmed the types of charges contained in the weapons (mainly TNT, RDX, HMX, and PETN; either as individual components or as mixtures). These energetic compounds were mainly detected as deprotonated species [M–H]−, or as adduct [M + 35Cl]−, [M + 37Cl]−, or [M + NO3]− anions. Chloride adducts were promoted in the heated DART reagent gas by adding chloroform vapors to the helium stream using an “in-house” delivery method. When the polarity was switched to positive mode, DART-HRMS revealed a very complex distribution of polymeric binders (mainly polyethylene glycols and polypropylene glycols), plasticizers (e.g., dioctyl sebacate, tributyl phosphate), as well as wax-like compounds whose structural features could not be precisely assigned. In positive mode, compounds were identified either as protonated molecules or ammonium adduct species. These results clearly demonstrate the complementarity of micro-Raman microscopy combined with DART-MS. The former technique provides structural information on the type of explosives present at the surface of the sample, whereas the latter provides not only a confirmation of the nature of the explosive charge but also useful additional information regarding the nature of the complex organic matrix of binders, plasticizers, polymers, oils, and potentially other organic additives and contaminants present in the sample. Combining these two techniques provides a powerful tool for the screening, comprehensive characterization, and differentiation of particulate explosive samples for forensic sciences and homeland security applications.Graphical Comprehensive characterization of explosive particles collected from swipe samples by micro-Raman and DART™-HRMSElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-016-9691-9) contains supplementary material, which is available to authorized users.

A Fast Liquid Chromatography Tandem Mass Spectrometric Analysis of PETN (Pentaerythritol Tetranitrate), RDX (3,5-Trinitro-1,3,5-triazacyclohexane) and HMX (Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) in Soil, Utilizing a Simple Ultrasonic-Assisted Extraction with Minimum Solvent

Direct analyses of explosives in soil using liquid chromatography tandem mass spectrometry (LC-MS/MS) methods are very limited in the literature and require complex procedures or relatively high amount of solvent. A simple and rapid method was developed for the determination of pentaerythritol tetranitrate (PETN), 3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), which are among the explosives used in terrorist attacks. A one-step extraction method for 1.00 g soil with 2.00 mL acetonitrile, and a 8-min LC-MS/MS method was developed. The detection limits for PETN, RDX and HMX were 5.2, 8.5 and 3.4 ng/g and quantitation limits were 10.0, 24.5, 6.0 ng/g. The intermediate precisions and Horwitz Ratio's were between 4.10 - 13.26% and 0.24 - 0.98, in order. This method was applied to a model post-blast debris collected from an artificial explosion and real samples collected after a terrorist attack in Istanbul. The method is easy and fast and requires less solvent use than other methods.

Contact between traps and surfaces during contact sampling of explosives in security settings

Realistic descriptions of interfacial contact between rough, deformable surfaces under load are difficult to obtain; however, this contact is of great import in a wide range of applications. Here, we detail, through experiment and computational simulation, the interfacial contact between four common traps and five commonly investigated surfaces encountered in explosives detection applications associated with airport security. The Young's modulus and hardness of four traps and seven substrates were measured using nanoindentation. These properties determine how deformation occurs when traps are applied for contact sampling of explosives. The nanoindentation data were analyzed using the Oliver-Pharr method, and an indenter area function was created using silicon and gold as the reference materials. The Young's moduli of the traps ranged from 0.2 to 8GPa, while those of the surfaces ranged from 0.5 to 4GPa. The hardness values of the traps ranged from 0.005 to 0.22GPa, while those of the surfaces ranged from 0.02 to 0.2GPa. For each of 20 scenarios (4 traps, 5 surfaces), six contact simulations were performed. In these contact simulations, the Greenwood-Willliamson microcontact model was used to represent the behavior of the asperities on the traps, while the Timoshenko Beam model was used to describe the macroscopic behavior of the bulk trap materials spanning the space between asperities. This combination of feature- and trap-scale modeling provides a more realistic description of the interfacial contact than either model applied individually. The calculated distributions of separation distances between the traps and surfaces when the traps were contacted with the surfaces under a normal load were compared to estimate the relative effectiveness of the traps at interrogating the topography of the surfaces. This method is proposed as a tool to guide the development of trap materials for surface sampling and surface cleaning applications.

Preshock Desensitization Phenomena during Initiation of Covered Heterogeneous Explosives by Shaped Charge Jets

The initiation of heterogeneous explosives by shaped charge jets is discussed. A reactive flow model, specially modified to account for the desensitization effects due to preshocking in heterogeneous explosives, is used to investigate the initiation of explosives by a shaped charge jet. Previously reported shaped charge jet initiation experimental setups are simulated using hydrodynamic software LS-DYNA with the desensitization model implemented as a user-defined equation of state. The simulation results indicate that the desensitization effects caused by the shocks preceding the jet play a significant role in determination of the run to detonation distance for covered explosives initiated by jets. The failure in initiation in the first explosive sample that is in contact with the steel plate and initiation of the second sample separated further by an air gap during penetration of the jet can be explained on the basis of desensitization phenomena. The simulation qualitatively reproduces various shock interaction phenomenon occurring in explosives during penetration by a shaped charge jet.

Shock to Initiation Characters of Heated Explosives with Different Confinement

AbstractHeated explosives might undergo thermal expansion and/or phase transition, which affects their shock sensitivity. Therefore, investigating the effect of temperature on the shock initiation properties of explosives would provide valuable safety guidelines for their transportation and handling. In this study, an experimental detonation device that achieved homogeneous heating of the explosive test sample while avoiding unintended heat transfer to the donor was designed and constructed. The device allowed to perform flyer impact tests on PBXC10 at different temperatures and using different confinement conditions. The generated experimental pressure history curves were used to calculate the parameters of the I&G model and determine their relationships with the sample temperature. The fully parameterized I&G model enabled predicting the shock initiation properties of PBXC10 at temperatures where experimental data were unavailable. It was concluded that increased sample temperatures would lead to a shorter run distance to detonation, faster propagation of the detonation wave and enhanced shock sensitivity of the explosive. It was also demonstrated that unconfined PBXC10 exhibited significantly greater shock sensitivity compared to its partially and completely confined counterparts.

Quantitative determination on binary-component polymer bonded explosives: A joint study of ultraviolet spectrophotometry and multivariate calibration methods

Explosive determination is of great importance in national defense and security fields. Simple, quick and reliable analytical techniques have been highly demanded in the field. In this work, we proposed a novel method for simultaneous determination of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinaitrotolunene (TNT) in binary-component polymer bonded explosive (PBX) samples by means of a combination of ultraviolet (UV) spectrophotometry with multivariable calibration methods. An orthogonal array design (DAD) was employed to construct the calibration set, which contains 27 reference samples. The calibration models were constructed using Partial Least Square regression (PLS-1) and Multiple Linear Regression (MLR). The variables were selected by the Successive Projection Algorithm (SPA) in MLR model. The predictive ability of the optimized models was validated by a test set including 18 samples. Finally, the two optimized models were successfully applied to simultaneously determine the content of PETN, RDX and TNT in five real binary-component PBX samples. Satisfactory results were obtained for the two models, in which the recovery yields were close to 100% for all the analytes. The computed elliptical joint confidence region (EJCR) further shows that the two models have no proportional and constant errors in the predicted concentrations. In addition, the statistical analysis indicates that MLR model with reasonable variable selection (SPA-MLR) could exhibit a slight superiority toward PLS-1 in the system. In a word, UV-spectroscopy in combination with multivariable calibration techniques has high potential to be a simple, quick and accurate analysis method for explosive determination in practice.

A New Reference Material and Safe Sampling of Terrorists Peroxide Explosives by a Non‐Volatile Matrix

AbstractHighly sensitive peroxide based explosives can be dissolved in ionic liquids for a safe handling. These solutions are easy to use and may be applied as powerful odor sources for analytical testing and training purposes. Moreover, the stabilizing effect of the ionic liquids can be exploited for a safe sampling of large quantities of these explosives. Such samples of triacetone triperoxide are long‐term stable, safe, and valid for forensic evaluations.

Analysis of underivatized cellodextrin oligosaccharides by capillary electrophoresis with direct photochemically induced UV-detection.

This work focuses on the development of a CE method allowing, for the first time, the simultaneous separation of the underivatized first seven cellodextrin oligomers (glucose, cellobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, and celloheptaose), with a view to analyze the hydrolysates obtained after partial acid depolymerization of nitrocellulose, and eight carbohydrates (ribose, xylose, fructose, mannose, galactose, maltose, lactose, and sucrose), which might be potential interfering compounds in explosives samples. Separation was achieved with a highly alkaline BGE containing sodium chloride and direct mid-UV-absorbance detection was performed after photo-oxidation in the detection window. EOF was reversed to speed up the analysis using a dynamic capillary coating by hexadimethrine bromide. A central composite design was carried out to determine the effects of BGE conductivity and sodium hydroxide concentration on resolutions between neighboring peaks, and analysis time. A desirability analysis on modeled responses was applied to maximize resolutions and to minimize analysis time. The simultaneous analysis in 20 min total runtime of the 15 carbohydrates plus internal reference (naphthalene sulfonate) was carried out at 25°C with a BGE composed of 77.4 mM NaOH and 183 mM NaCl to adjust the conductivity at the optimum value. Finally, the resolution robustness was checked. This new method should also be of interest to monitor food and nonfood crop products.

Rapid and Specific Aqueous-Phase Detection of Nitroaromatic Explosives with Inherent Porphyrin Recognition Sites in Metal-Organic Frameworks.

Development of a rapid and effective method for the detection of 2,4,6-trinitrotoluene (TNT) in aqueous phase has attracted great attention. In this work, the fluorescent porphyrin-based metal-organic frameworks (MOFs) of PCN-224 were successfully exploited as a fluorescent probe for the rapid and selective TNT detection in water media. This strategy combined the advantages of fluorescent porphyrin molecules and porous MOFs, which not only overcame the aggregation of hydrophobic tetrakis(4-carboxyphenyl)porphyrin (TCPP) recognition sites but also promoted TNT to interact with recognition sites in virtue of the high surface and intrinsic open structure of MOFs. As a result, a rapid response time of as short as 30 s was obtained for the elaborated fluorescent probe. Meanwhile, the bright red emission of porphyrin units in PCN-224 could be proportionally quenched in correlation with the applied TNT level through the formation of TNT-TCPP complex in the ground state. The specificity of the employed sensory platform for TNT recognition was scarcely affected by other possible coexistent interfering species. Furthermore, this fluorescent PCN-224 probe presented a much higher quenching efficiency for TNT than other structurally similar nitroaromatic compounds and was successfully applied for the quantitative detection of TNT in the mixed nitroaromatic explosive samples. This prefigured their great potentials of practical TNT detection in water media for public safety and security.

Fast Chromatographic Method for Explosive Profiling

Security control is becoming a major global issue in strategic locations, such as airports, official buildings, and transit stations. The agencies responsible for public security need powerful and sensitive tools to detect warfare agents and explosives. Volatile signature detection is one of the fastest and easiest ways to achieve this task. However, explosive chemicals have low volatility making their detection challenging. In this research, we developed and evaluated fast chromatographic methods to improve the characterization of volatile signatures from explosives samples. The headspace of explosives was sampled with solid phase micro-extraction fiber (SPME). Following this step, classical gas chromatography (GC) and comprehensive two-dimensional GC (GC×GC) were used for analysis. A fast GC approach allows the elution temperature of each analyte to be decreased, resulting in decreased thermal degradation of sensitive compounds (e.g., nitro explosives). Using fast GC×GC, the limit of detection is further decreased based on the cryo-focusing effect of the modulator. Sampling of explosives and chromatographic separation were optimized, and the methods then applied to commercial explosives samples. Implementation of fast GC methods will be valuable in the future for defense and security forensics applications.

Multivariate optimization of the denitration reaction of nitrocelluloses for safer determination of their nitrogen content

The nitrogen content is of paramount importance to predict the explosive or non-explosive character of nitrocellulose (NC), and hence its applications. There are still quite a few really effective analytical methodologies allowing its determination, due to great NC molecular complexity. One of the approaches giving access to nitrogen content consists in releasing the nitrogenic moieties through alkaline hydrolysis. For the first time, this work reports on the optimization of the denitration yield by means of an experimental design within reasonable ranges of sodium hydroxide concentration, temperature, and time. The experiments were conducted with non-explosive and explosive NC standards. An original capillary electrophoresis (CE) method was used to monitor nitrite and nitrate ions released during hydrolysis. Because of their very different chemical properties, denitration conditions were optimized separately for both sub-classes of NCs to maximize their denitration yields, applying desirability analysis on modeled denitration yields. Mild, safe, and robust optimized conditions were drawn. The denitration yields (95% for non-explosive NCs, 92% for explosive NCs) experimentally obtained under these conditions were in good agreement with model predictions. For practical purposes, correction factors based on these maximal denitration yields are proposed for the first time to correct the determination of nitrogen content, based on preliminary alkaline denitration. This new strategy was successfully applied to determine nitrogen contents of NCs in real explosive samples (smokeless gunpowders).

Terahertz spectrum and simulation of the phase transformation of FOX-7

1, 1-diamino-2, 2-dintroethylene (FOX-7) is a novel explosive of high energy and low sensibility. In order to study the effect of temperature changes on the molecular structural characteristics of the explosive, its absorption spectra in the frequency range of 0.2–2.5 THz at a constant rate of heating from 298 K to 393 K are detected by terahertz time-domain spectroscopy (THz-TDS). Results show that a number of characteristic absorption peaks with different intensities appear at 1.59–2.13 THz when the temperature is 298 K, while the absorption spectra change with the increase of temperature of the explosive sample; a new characteristic absorption peak located at 1.12 THz appears at 384 K, and its absorption peak intensity gradually increases, but disappears when the temperature drops to 298 K. The absorption spectra of FOX-7 molecular crystal at 298 and 393 K within the 0.2–2.5 THz region based on density functional theory (DFT) are also simulated by using Materials Studio 6.0 software in this article, and the simulated results agree well with the experimental data. In addition, the vibrational modes of the characteristic peaks of two kinds of crystalline in the experimental absorption spectra are analyzed and identified, showing that the formation of the characteristic absorption peaks is closely related to the molecular vibration, and the molecular structure may change under the influence of temperature, and the tautomeric polymorphism of the crystalline has different vibrational modes. This article indicates that the process of phase transformation of FOX-7 starts from 384 K, and this process is reversible; the characteristic absorption peak at 1.12 THz is composed of two kinds of vibrations (the swinging and torsional vibrations of the nitro and amido groups).

A new method for the determination of the nitrogen content of nitrocellulose based on the molar ratio of nitrite-to-nitrate ions released after alkaline hydrolysis

A new method was proposed to determine the nitrogen content of nitrocelluloses (NCs). It is based on the finding of a linear relationship between the nitrogen content and the molar ratio of nitrite-to-nitrate ions released after alkaline hydrolysis. Capillary electrophoresis was used to monitor the concentration of nitrite and nitrate ions. The influences of hydrolysis time and molar mass of NC on the molar ratio of nitrite-to-nitrate ions were investigated, and new insights into the understanding of the alkaline denitration mechanism of NCs, underlying this analytical strategy is provided. The method was then tested successfully with various explosive and non-explosive NC-containing samples such as various daily products and smokeless gunpowders. Inherently to its principle exploiting a concentration ratio, this method shows very good repeatability in the determination of nitrogen content in real samples with relative standard deviation (n=3) inferior to 1.5%, and also provides very significant advantages with respect to sample extraction, analysis time (1h for alkaline hydrolysis, 3min for electrophoretic separation), which was about 5 times shorter than for the classical Devarda's method, currently used in industry, and safety conditions (no need for preliminary drying NC samples, mild hydrolysis conditions with 1M sodium hydroxide for 1h at 60°C).

Effects of oil pipeline explosion on ambient particulate matter and their associated polycyclic aromatic hydrocarbons

Effects of the oil pipeline explosion on PM2.5-associated polycyclic aromatic hydrocarbons (PAHs) and their substituted (alkylated, nitrated, oxygenated, hydroxyl and chlorinated) derivatives are assessed near the accident scene of Qingdao, China. Compared with those in TSP-PM2.5, gaseous phase, burn residue and unburned crude oil, eighty-nine PAHs in PM2.5 are identified and quantified to investigate the composition, temporal and spatial distribution, and sources. The concentrations of PM2.5-associated parent PAHs increase approximately seven times from the non-explosion samples to the explosion samples (mean ± standard deviation: 112 ± 2 vs 764 ± 15 ng/m3), while some substituted products (nitro- and oxy-) increase by two orders of magnitude (3117 ± 156 pg/m3 vs 740 ± 37 ng/m3). The toxicity evaluation indicates the BaP equivalent concentrations (based on the US EPA's toxicity factors) in PM2.5 are much higher than those in the other phases, especially for a long duration after the tragic accident.

Cavitand-Based Solid-Phase Microextraction Coating for the Selective Detection of Nitroaromatic Explosives in Air and Soil

A selective cavitand-based solid-phase microextraction coating was synthesized for the determination of nitroaromatic explosives and explosive taggants at trace levels in air and soil. A quinoxaline cavitand functionalized with a carboxylic group at the upper rim was used to enhance selectivity toward analytes containing nitro groups. The fibers were characterized in terms of film thickness, morphology, thermal stability, and pH resistance. An average coating thickness of 50 (±4) μm, a thermal stability until 400 °C, and an excellent fiber-to-fiber and batch to batch repeatability with RSD lower than 4% were obtained. The capabilities of the developed coating for the selective sampling of nitroaromatic explosives were proved achieving LOD values in the low ppbv and ng kg(-1) range, respectively, for air and soil samples.

Explosive origin of silicic lava: Textural and [formula omitted]–H2O evidence for pyroclastic degassing during rhyolite effusion

A long-standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava. A widely cited idea is that the explosive-to-effusive transition manifests a two-stage degassing history whereby lava is the product of non-explosive, open-system gas release following initial explosive, closed-system degassing. Direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive, as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent. This explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava. Here we use precise H-isotope and magmatic H2O measurements and textural evidence to demonstrate that effusion results from explosion(s)—lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels (tuffisites) that repetitively and explosively vent from effusing lava. Our measurements show, specifically that D/H ratios and H2O contents of a broad suite of explosive and effusive samples from Chaitén volcano (hydrous bombs, Plinian pyroclasts, tuffisite veins, and lava) define a single and continuous degassing trend that links wet explosive pyroclasts (∼1.6 wt.% H2O, δD=−76.4‰) to dry obsidian lavas (∼0.13 wt.% H2O, δD=−145.7‰). This geochemical pattern is best fit with batched degassing model that comprises small repeated closed-system degassing steps followed by pulses of vapour extraction. This degassing mechanism is made possible by the action of tuffisite veins, which, by tapping already vesicular or brecciated magma, allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed-system domains and large tracts of conduit magma by giving them long-range connectivity. Even though tuffisite veins render magma degassed and capable of effusing, they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut. Thus the effusion of silicic lava, traditionally thought to be relatively benign process, presents a particularly hazardous form of explosive volcanism.

Explosive to effusive transition during the largest volcanic eruption of the 20th century (Novarupta 1912, Alaska)

Silicic volcanic eruptions commonly show abrupt shifts between powerful and dangerous (Plinian) explosive episodes and gentle effusion of lava. Whether the onset of magma permeability and ensuing gas loss controls these transitions has been a subject of debate. We measured porosities and permeabilities in samples from the A.D. 1912 eruption of Novarupta volcano, Alaska, and analyzed them within the context of a well-constrained eruptive sequence that encompasses sustained explosive and effusive activity. For the explosive samples, we find that the degree of vesicle interconnectivity, measured as the ratio of connected to total porosity, decreases with phenocryst content and with increasing eruption intensity. Permeabilities of explosive samples show a weak dependence on porosity. Dome samples are not significantly different in permeability, but are of lower porosity, which together with abundant flattened vesicles is consistent with bubble collapse by permeable outgassing. Quantitative analysis indicates that outgassing alone was insufficient to affect the transition to effusive activity. Rather, the change from explosive to effusive activity was probably a consequence of high versus low magma ascent rates.

Quantitative detection of trace explosive vapors by programmed temperature desorption gas chromatography-electron capture detector.

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive vapor samples. The direct liquid deposition method yields a higher fidelity between the analysis of vapor samples and the analysis of solution standards than using separate injection methods for vapors and solutions, i.e., samples collected on vapor collection tubes and standards prepared in solution vials. Additionally, the method can account for instrumentation losses, which makes it ideal for minimizing variability and quantitative trace chemical detection. Gas chromatography with an electron capture detector is an instrumentation configuration sensitive to nitro-energetics, such as TNT and RDX, due to their relatively high electron affinity. However, vapor quantitation of these compounds is difficult without viable vapor standards. Thus, we eliminate the requirement for vapor standards by combining the sensitivity of the instrumentation with a direct liquid deposition protocol to analyze trace explosive vapor samples.

Effects of scale on internal blast measurements

This paper presents a comparative study between large and small-scale internal blast experiments with the goal of using the small-scale analog for energetic performance evaluation. In the small-scale experiment, highly confined explosive samples <0.5 g were subjected to the output from a PETN detonator while enclosed in a 3-liter chamber. Large-scale tests up to 23 kg were unconfined and released in a chamber with a factor of 60,000 increase in volume. The comparative metric in these experiments is peak quasi-static overpressure, with the explosive sample expressed as sample energy/chamber volume, which normalizes measured pressures across scale. Small-scale measured pressures were always lower than the large-scale measurements, because of heat-loss to the high confinement inherent in the small-scale apparatus. This heat-loss can be quantified and used to correct the small-scale pressure measurements. In some cases the heat-loss was large enough to quench reaction of lower energy samples. These results suggest that small-scale internal blast tests do correlate with their large-scale counterparts, provided that heat-loss to confinement can be measured, and that less reactive or lower energy samples are not quenched by heat-loss.

The increased shock sensitivity of PBX 9502 at high temperature

A modified gap test using brass attenuators has been designed that can significantly heat explosive samples prior to testing. The sensitivity of PBX 9502 when heated to 180, 200, 230 & 260°C and soaked for 30 minutes was investigated. It was discovered that under the moderate confinement (0.46 MPa) of this test, the sensitivity of the material did increase close to literature data for LX-17 (a very similar composition) heated to 250°C under numerically unquantified 'heavy confinement'.