Explosive-related Compounds Research Articles

Identification of Absorption Spectrum for IED Precursors Using Laser Photoacoustic Spectroscopy.

Among the many commonly encountered hazards, improvised explosive devices (IEDs) remain the primary threat to military and civilian personnel due to the ease of their production and the widespread availability of their raw materials and precursors. Identifying traces of potential precursors is the first step in developing appropriate control measures. An interesting approach is to identify the precursors that are released around the site as they are handled and transformed into the final IEDs. CO2 laser photoacoustic spectroscopy can offer the spectral characterization of a number of explosives-related compounds without sample preparation. Benzene, toluene, acetone, and ethylene glycol absorption spectra were determined in the IR region between 9.2 and 10.8 µm. Each substance emitted a unique photoacoustic response corresponding to its chemical composition that could be further used to identify the explosive material.

Optimization of gas chromatography/vacuum ultraviolet (GC/VUV) spectroscopy for explosive compounds and application to post-blast debris

A statistical optimization of gas chromatography/vacuum ultraviolet spectroscopy (GC/VUV) for the analysis of explosives has yet to be presented. In this work, a central composite design of experiments was utilized to optimize GC/VUV parameters for explosive and explosive related compounds such as triacetone triperoxide (TATP), dimethyldinitrobutane (DMNB), nitroglycerine (NG), diphenylamine (DPA), 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and cyclonite (RDX). Parameters optimized include the final temperature of a ramped multimode inlet program (200 °C), GC carrier gas flow rate (1.9 mL/min), and VUV make-up gas pressure (0.00 psi). The impact of transfer line/flow cell temperature was determined not to be statistically significant. Post-blast debris was successfully analyzed to illustrate applicability to forensic analysis of explosives. Relevant compounds in single- and double-base smokeless powders were successfully identified in post-blast fragments originating from PVC and steel pipes.

Optimization of ultraviolet Raman spectroscopy for trace explosive checkpoint screening.

Raman spectroscopy has long been considered a gold standard for optically based chemical identification, but has not been adopted in non-laboratory operational settings due to limited sensitivity and slow acquisition times. Ultraviolet (UV) Raman spectroscopy has the potential to address these challenges through the reduction of fluorescence from background materials and increased Raman scattering due to the shorter wavelength (relative to visible or near-infrared excitation) and resonant enhancement effects. However, the benefits of UV Raman must be evaluated against specific operational situations: the actual realized fluorescence reduction and Raman enhancement depend on the specific target materials, target morphology, and operational constraints. In this paper, the wavelength trade-space in UV Raman spectroscopy is evaluated for one specific application: checkpoint screening for trace explosive residues. The optimal UV wavelength is evaluated at 244, 266, and 355nm for realistic trace explosive and explosive-related compound (ERC) residues on common checkpoint materials: we perform semi-empirical analysis that includes the UV penetration depth of common explosive and ERCs, realistic explosive and ERC residue particle sizes, and the fluorescence signal of common checkpoint materials. We find that while generally lower UV wavelength provides superior performance, the benefits may be significantly reduced depending on the specific explosive and substrate. Further, logistical requirements (size, weight, power, and cost) likely limit the adoption of optimal wavelengths. Graphical abstract.

Field demonstration of portable vapor sampling in a simulated cargo container

Screening technologies are necessary to counteract illegal trafficking through ports of entry in the United States and internationally. Here we present results from initial field testing of a recently-developed portable vapor sensing unit, portable PLOT (porous layer open tubular)-cryoadsorption. A surplus US Army bunker was used as a simulated cargo container, and four sets of experiments demonstrated the unit’s functionality in a field environment. Three chemical mixtures acted as surrogates for materials relevant to screening operations: explosives-related compounds, protein decomposition compounds, and gasoline. In this feasibility study, portable PLOT-cryoadsorption successfully collected components of each mixture in a variety of weather conditions and with short vapor collection times well suited to a field environment. Gas chromatography with mass spectrometry (GC–MS) was used for sample analysis.

The analysis of nitrate explosive vapour samples using Lab-on-a-chip instrumentation

The detection and analysis of explosives and explosive-related compounds is a heightened priority in recent years for homeland security and counter-terrorism applications. This study aimed to evaluate the use of a commercial Lab-On-a-Chip (LOC) instrument for the analysis of explosive vapours, with the long-term goal of developing a portable instrument for passively detecting explosives in air samples. A simple method to collect explosive vapour residues was developed using a glass vial containing varying amounts of the target explosives (1 mg/mL). Standards were diluted to the desired concentration in 150 μL of acetone to facilitate the evaporation. The top of the vial was covered with a circular 0.5 cm diameter filter paper and exposed to a range of temperatures from 22 °C to 80 °C for 15 min. Following evaporation, the filter paper chads were folded and inserted into the LOC wells containing the separation buffer for the analysis, avoiding any further extraction step. After successfully separating and detecting eight explosives via liquid analysis, three explosives were chosen as targets for the vapour analysis experiments. 1,3,5-Trinitrobenzene (TNB), 2,4,6-Trinitrotoluene (TNT), and 2,4,6-Trinitrophenylmethylnitramine (Tetryl) were successfully separated, detected and identified following the vapour extraction of explosive standards onto filter paper chads. Limits of detection for the liquid analysis were demonstrated to be 2.32 ng for TNB, 2.35 ng for Tetryl, and 3.25 ng for TNT. The minimum detectable mass found for the vapour analysis was 6.03 for TNB, 9.99 ng for TNT, and 14.22 ng for Tetryl. The average recovery from the paper chads was 29% for Tetryl, 47% for TNB, and 75% for TNT (n = 4), comparable with findings from previous studies. Results show that a minimum temperature of 40 °C is necessary to vaporize the compounds using acetone, while the best results were achieved when heating the vial to 80 °C. The use of a filter paper to collect the explosives residues, avoiding any additional extraction step, and the ability to analyze these compounds using a LOC instrument, makes this approach a future alternative method for explosive residues detection in the headspace.

Sorbent Film-Coated Passive Samplers for Explosives Vapour Detection Part A: Materials Optimisation and Integration with Analytical Technologies

A new thin-film passive sampler is presented as a low resource dependent and discrete continuous monitoring solution for explosives-related vapours. Using 15 mid-high vapour pressure explosives-related compounds as probes, combinations of four thermally stable substrates and six film-based sorbents were evaluated. Meta-aramid and phenylene oxide-based materials showed the best recoveries from small voids (~70%). Analysis was performed using liquid chromatography-high resolution accurate mass spectrometry which also enabled tentative identification of new targets from the acquired data. Preliminary uptake kinetics experiments revealed plateau concentrations on the device were reached between 3–5 days. Compounds used in improvised explosive devices, such as triacetone triperoxide, were detected within 1 hour and were stably retained by the sampler for up to 7 days. Sampler performance was consistent for 22 months after manufacture. Lastly, its direct integration with currently in-service explosives screening equipment including ion mobility spectrometry and thermal desorption mass spectrometry is presented. Following exposure to several open environments and targeted interferences, sampler performance was subsequently assessed and potential interferences identified. High-security building and area monitoring for concealed explosives using such cost-effective and discrete passive samplers can add extra assurance to search routines while minimising any additional burden on personnel or everyday site operation.

Development and validation of a solid phase extraction sample cleanup procedure for the recovery of trace levels of nitro-organic explosives in soil

An improved cleanup method has been developed for the recovery of trace levels of 12 nitro-organic explosives in soil, which is important not only for the forensic community, but also has environmental implications. A wide variety of explosives or explosive-related compounds were evaluated, including nitramines, nitrate esters, nitroaromatics, and a nitroalkane. Fortified soil samples were extracted with acetone, processed via solid phase extraction (SPE), and then analyzed by gas chromatography with electron capture detection. The following three SPE sorbents in cartridge format were compared: Empore™ SDB-XC, Oasis® HLB, and Bond Elut NEXUS cartridges. The NEXUS cartridges provided the best overall recoveries for the 12 explosives in potting soil (average 48%) and the fastest processing times (<30min). It also rejected matrix components from spent motor oil on potting soil. The SPE method was validated by assessing limit of detection (LOD), processed sample stability, and interferences. All 12 compounds were detectable at 0.02μg explosive/gram of soil or lower in the three matrices tested (potting soil, sand, and loam) over three days. Seven explosives were stable up to seven days at 2μg/g and three were stable at 0.2μg/g, both in processed loam, which was the most challenging matrix. In the interference study, five interferences above the determined LOD for soil were detected in matrices collected across the United States and in purchased all-purpose sand, potting soil, and loam. This represented a 3.2% false positive rate for the 13 matrices processed by the screening method for interferences. The reported SPE cleanup method provides a fast and simple extraction process for separating organic explosives from matrix components, facilitating sample throughput and reducing instrument maintenance. In addition, a comparison study of the validated SPE method versus conventional syringe filtration was completed and highlighted the benefits of sample cleanup for removing matrix interferences, while also providing lower supply cost, order of magnitude lower LODs for most explosives, higher percent recoveries for complex matrices, and fewer instrument maintenance issues.

A New Type of Explosive Chemical Detector Based on an Organic Photovoltaic Cell

A new type of chemical sensor to detect explosive related compounds has been designed and fabricated with an organic photovoltaic cell as the active element. The detection of chemical molecules is performed by optically exciting the cell while its photovoltaic open-circuit voltage is continuously sampled. Upon exposure to compounds like nitroaromatics, the sensors exhibit a significant increase in open-circuit voltage. This indicates an efficient internal energy transfer between the explosive chemicals and the organic thin film surface. It is quite unique that the organic chemical sensors directly use the open-circuit voltage as a detection indicator, while the vast majority of conventional chemical sensors are based on the change in resistance. Since the open-circuit voltage can be measured without current and can also be directly sampled or amplified in the circuits, this new type of chemical sensor is very attractive for low-power application and sensor networks for the future Internet of Things.

Rapid identification and desorption mechanisms of nitrogen-based explosives by ambient micro-fabricated glow discharge plasma desorption/ionization (MFGDP) mass spectrometry

A novel technique of micro-fabricated glow discharge plasma desorption/ionization mass spectrometry was investigated for the first time in negative ion mode in this study. Negative ion micro-fabricated glow discharge plasma desorption/ionization mass spectrometry (NI-MFGDP-MS) was successfully applied to identify trace explosives in open air. Six explosives and explosives-related compounds were directly analyzed in seconds with this ion source. The ions of [M-H]- were predominant for 2-methyl-1,3,5-trinitrobenzene (trinitrotoluene, TNT) and 2,4,6-trinitrophenol (picric acid), and [M+NO3]- were dominant ions for 1,3,5-trinitro-perhydro-1,3,5-triazine (cyclonite, RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (octogen, HMX), 1,2,3-trinitroxypropane (nitroglycerin, NG), and pentaerythritol tetranitrate (PETN). The limits of detection (LOD) were from 87.5pgmm−2 to 0.4 fg mm−2 and the relative standard deviation (RSD) ranged between 5.8% and 16.8% for the explosives involved in this study. The reliability of NI-MFGDP-MS was characterized by the analysis of a picric acid-RDX-PETN mixture and a mixture of RDX-pond water. NI-MFGDP-MS and ESI-MS were compared with these explosives and along with collision induced dissociation (CID) experiments. The results showed that electron capture, proton abstraction reaction, nucleophilic attack, ion–molecule attachment, decomposition and anion attachment took place during the NI-MFGDP-MS measurement. These findings provide a guideline and a supplement to the chemical libraries for rapid and accurate detection of explosives. The method shows great potential for fast, in situ, on-line and high throughput detection of explosives in the field of antiterrorism.

Suspect screening and quantification of trace organic explosives in wastewater using solid phase extraction and liquid chromatography-high resolution accurate mass spectrometry

The first comprehensive assessment of 34 solid phase extraction sorbents is presented for organic explosive residues in wastewater prior to analysis with liquid chromatography-high resolution accurate mass spectrometry (LC-HRMS). A total of 18 explosives were selected including nitramines, nitrate esters, nitroaromatics and organic peroxides. Three polymeric divinylbenzene-based sorbents were found to be most suitable and one co-polymerised with n-vinyl pyrrolidone offered satisfactory recoveries for 14 compounds in fortified wastewater (77–124%). Limits of detection in matrix ranged from 0.026–23μgL−1 with R2≥0.98 for most compounds. The method was applied to eight 24-h composite wastewater samples from a London wastewater works and one compound, 2,4-dinitrotoluene, was determined over five days between 332 and 468g day−1 (225–303ngL−1). To further exploit the suspect screening capability, 17 additional explosives, precursors and transformation products were screened in spiked wastewater samples. Of these, 14 were detected with recoveries from 62 to 92%, highlighting the broad applicability of the method. To our knowledge, this represents the first screen of explosives-related compounds in wastewater from a major European city. This method also allows post-analysis detection of new or emerging compounds using full-scan HRMS datasets to potentially identify and locate illegal manufacture of explosives via wastewater analysis.

Instant detection and identification of concealed explosive-related compounds: Induced Stokes Raman versus infrared

The instant detection of explosives and explosive-related compounds has become an urgent priority in recent years for homeland security and counter-terrorism applications. Modern techniques should offer enhancement in selectivity, sensitivity, and standoff distances. Miniaturisation, portability, and field-ruggedisation are crucial requirements. This study reports on instant and standoff identification of concealed explosive-related compounds using customized Raman technique. Stokes Raman spectra of common explosive-related compounds were generated and spectrally resolved to create characteristic finger print spectra. The scattered Raman emissions over the band 400:2000cm−1 were compared to infrared absorption using FTIR. It has been demonstrated that the two vibrational spectroscopic techniques were opposite and completing each other. Molecular vibrations with strong absorption in infrared (those involve strong change in dipole moments) induced weak signals in Raman and vice versa. The tailored Raman offered instant detection, high sensitivity, and standoff detection capabilities. Raman demonstrated characteristic fingerprint spectra with stable baseline and sharp intense peaks. Complete correlations of absorption/scattered signals to certain molecular vibrations were conducted to generate an entire spectroscopic profile of explosive-related compounds. This manuscript shades the light on Raman as one of the prevailing technologies for instantaneous detection of explosive-related compounds.

Contributed review: quantum cascade laser based photoacoustic detection of explosives.

Detecting trace explosives and explosive-related compounds has recently become a topic of utmost importance for increasing public security around the world. A wide variety of detection methods and an even wider range of physical chemistry issues are involved in this very challenging area. Optical sensing methods, in particular mid-infrared spectrometry techniques, have a great potential to become a more desirable tools for the detection of explosives. The small size, simplicity, high output power, long-term reliability make external cavity quantum cascade lasers (EC-QCLs) the promising spectroscopic sources for developing analytical instrumentation. This work reviews the current technical progress in EC-QCL-based photoacoustic spectroscopy for explosives detection. The potential for both close-contact and standoff configurations using this technique is completely presented over the course of approximately the last one decade.

Differentiation of isomeric dinitrotoluenes and aminodinitrotoluenes using electrospray high resolution mass spectrometry.

Explosive detection and identification play an important role in the environmental and forensic sciences. However, accurate identification of isomeric compounds remains a challenging task for current analytical methods. The combination of electrospray multistage mass spectrometry (ESI-MS(n) ) and high resolution mass spectrometry (HRMS) is a powerful tool for the structure characterization of isomeric compounds. We show herein that resonant ion activation performed in a linear quadrupole ion trap allows the differentiation of dinitrotoluene isomers as well as aminodinitrotoluene isomers. The explosive-related compounds: 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 2-amino-4,6-dinitrotoluene (2A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) were analyzed by ESI-MS in the negative ion mode; they produced mainly deprotonated molecules [M - H](-) . Subsequent low resolution MS(n) experiments provided support for fragment ion assignments and determination of consecutive dissociation pathways. Resonant activation of deprotonated dinitrotoluene isomers gave different fragment ions according to the position of the nitro and amino groups on the toluene backbone. Fragment ion identification was bolstered by accurate mass measurements performed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Notably, unexpected results were found from accurate mass measurements performed at high resolution for 2,6-DNT where a 30-Da loss was observed that corresponds to CH2 O departure instead of the expected isobaric NO(•) loss. Moreover, 2,4-DNT showed a diagnostic fragment ion at m/z 116, allowing the unambiguous distinction between 2,4- and 2,6-DNT isomers. Here, CH2 O loss is hindered by the presence of an amino group in both 2A-4,6-DNT and 4A-2,6-DNT isomers, but nevertheless, these isomers showed significant differences in their fragmentation sequences, thus allowing their differentiation. DFT calculations were also performed to support experimental observations.

Chromatographic Air Analyzer Microsystem for the Selective and Sensitive Detection of Explosive-related Compounds

Abstract The detection of explosives and explosive-related compounds is of major importance for the monitoring of explosive- contaminated sites. Current methods need to become cheaper and portable while maintaining a high sensitivity and selectivity level. In that sense, a silicon micro-analytical platform consisting of a three-dimensional micro-preconcentrator based on a hydrophobic zeolite, coupled to a silicon spiral micro-column was built. A chemical gas sensor acted as a miniaturized gas detector. This system allowed selective detection of orthonitrotoluene (ONT), an explosive-related compound at the sub-ppm level in the presence of toluene and moisture.

Development of a micro-analytical prototype for selective trace detection of orthonitrotoluene

A silicon micro-analytical platform consisting of a micro-preconcentrator based on a hydrophobic zeolite, coupled to a silicon spiral micro-column was built. A chemical gas sensor acted as a miniaturized gas detector. This system allowed selective detection of orthonitrotoluene (ONT), an explosive-related compound at the sub-ppm level (365ppb) in the presence of toluene and moisture.

Spectroscopic observation of neutral carbon during photodissociation of explosive-related compounds in the vapor phase

We perform time-resolved laser-induced fluorescence measurements of mononitrotoluenes (MNTs) and dinitrotoluenes (DNTs) in nitrogen and air. We observe the multipeak emission spectrum of NO and find that the emission peak intensity in the 247-248nm range is stronger than expected compared to the other NO emission peak intensities. This increased emission intensity is believed to be due to neutral carbon [C(I)], which has a strong emission peak at 247.85nm. By comparing the ratios of integrated emission peak intensities with those expected from the Franck-Condon factors for NO, we are able to identify samples that exhibit C(I) emission. We show that the DNTs exhibit C(I) emission for gate delays of 1500ns and beyond, while the MNTs exhibit C(I) emission for gate delays of only up to about 500ns. Carbon deposits in the analysis chamber confirm the presence of C. Ambient NO in air enhances the observed NO+C(I) signal from MNTs and DNTs.

Selection and characterization of adsorbents for the analysis of an explosive-related molecule traces in the air

This study is focused on the development of a 3D micro-preconcentrator for a sensitive analysis of an explosive-related compound: orthonitrotoluene (ONT). A set of potentially efficient adsorbents for the pre-concentration of ONT was investigated here. An in-depth characterization of their textural properties was carried out in order to better understand their adsorption behavior toward the target analyte. More particularly, this study allowed highlighting the interesting adsorption features of a hydrophobic zeolite and a porous activated carbon in relation to their preconcentration performances toward ONT at the ppb level. Moreover, we found a difference in the adsorption mechanism between both selected adsorbing materials.

Noninvasive Detection of Concealed Explosives: Depth Profiling through Opaque Plastics by Time-Resolved Raman Spectroscopy

The detection of explosives concealed behind opaque, diffusely scattering materials is a challenge that requires noninvasive analytical techniques for identification without having to manipulate the package. In this context, this study focuses on the application of time-resolved Raman spectroscopy (TRRS) with a picosecond pulsed laser and an intensified charge-coupled device (ICCD) detector for the noninvasive identification of explosive materials through several millimeters of opaque polymers or plastic packaging materials. By means of a short (250 ps) gate which can be delayed several hundred picoseconds after the laser pulse, the ICCD detector allows for the temporal discrimination between photons from the surface of a sample and those from deeper layers. TRRS was applied for the detection of the two main isomers of dinitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene as well as for various other components of explosive mixtures, including akardite II, diphenylamine, and ethyl centralite. Spectra were obtained through different diffuse scattering white polymer materials: polytetrafluoroethylene (PTFE), polyoxymethylene (POM), and polyethylene (PE). Common packaging materials of various thicknesses were also selected, including polystyrene (PS) and polyvinyl chloride (PVC). With the demonstration of the ability to detect concealed, explosives-related compounds through an opaque first layer, this study may have important applications in the security and forensic fields.

Detection of Explosives and Related Compounds by Low-Temperature Plasma Ambient Ionization Mass Spectrometry

Detection of explosives is important for public safety. A recently developed low-temperature plasma (LTP) probe for desorption and ionization of samples in the ambient environment ( Anal. Chem. 2008 , 80 , 9097 ) is applied in a comprehensive evaluation of analytical performance for rapid detection of 13 explosives and explosives-related compounds. The selected chemicals [pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), cyclo-1,3,5-trimethylenetrinitramine (RDX), tetryl, cyclo-1,3,5,7-tetramethylenetetranitrate (HMX), hexamethylene triperoxide diamine (HMTD), 2,4-dinitrotoluene, 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,6-dinitrotoluene, and 4-nitrotoluene) were tested at levels in the range 1 pg-10 ng. Most showed remarkable sensitivity in the negative-ion mode, yielding limits of detection in the low picogram range, particularly when analyzed from a glass substrate heated to 120 °C. Ions typically formed from these molecules (M) by LTP include [M + NO(2)](-), [M](-), and [M - NO(2)](-). The LTP-mass spectrometry methodology displayed a linear signal response over three orders of magnitude of analyte amount for the studied explosives. In addition, the effects of synthetic matrices and different types of surfaces were evaluated. The data obtained demonstrate that LTP-MS allows detection of ultratrace amounts of explosives and confirmation of their identity. Tandem mass spectrometry (MS/MS) was used to confirm the presence of selected explosives at low levels; for example, TNT was confirmed at absolute levels as low as 0.6 pg. Linearity and intra- and interday precision were also evaluated, yielding results that demonstrate the potential usefulness and ruggedness of LTP-MS for the detection of explosives of different classes. The use of ion/molecule reactions to form adducts with particular explosives such as RDX and HMX was shown to enhance the selectivity and specificity. This was accomplished by merging the discharge gas with an appropriate reagent headspace vapor (e.g., from a 0.2% trifluoracetic acid solution).

Fluorescent Polymer Sensor Array for Detection and Discrimination of Explosives in Water

A fluorescent polymer sensor array (FPSA) was made from commercially available fluorescent polymers coated onto glass beads and was tested to assess the ability of the array to discriminate between different analytes in aqueous solution. The array was challenged with exposures to 17 different analytes, including the explosives trinitrotoluene (TNT), tetryl, and RDX, various explosive-related compounds (ERCs), and nonexplosive electron-withdrawing compounds (EWCs). The array exhibited a natural selectivity toward EWCs, while the non-electron-withdrawing explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) produced no response. Response signatures were visualized by principal component analysis (PCA), and classified by linear discriminant analysis (LDA). RDX produced the same response signature as the sampled blanks and was classified accordingly. The array exhibited excellent discrimination toward all other compounds, with the exception of the isomers of nitrotoluene and aminodinitrotoluene. Of particular note was the ability of the array to discriminate between the three isomers of dinitrobenzene. The natural selectivity of the FPSA toward EWCs, plus the ability of the FPSA to discriminate between different EWCs, could be used to design a sensor with a low false alarm rate and an excellent ability to discriminate between explosives and explosive-related compounds.