Canines are widely used for real-time detection of explosives and have proven to be on par with instrumental methods. Canines are thought to rely largely upon detection of volatile chemical ...constituents of the explosives, though not necessarily the explosive itself. Hence, it is crucial to understand the odor available to them as generated by training aids. Previous studies have established that the Training Aid Delivery Device (TADD) developed by SciK9 is a reliable training aid that reduces cross-contamination and doubles as a storage device. A TADD comprises a standardized container, a synthetic membrane, a membrane holder, and a lid. In the work presented, activated charcoal strips were placed above and below the TADD membrane to determine the relative amounts of volatiles emitted by dynamite (i.e., ethylene glycol dinitrate (EGDN) and trinitroglycerin (NG)). The strips were eluted and the extracts tested using gas chromatography-mass spectrometry in negative ion chemical ionization mode. A series of t-tests at 95% confidence level were performed to determine any differences in vapor composition above and below the membranes. Nine synthetic membranes and six glass fiber membranes were tested in this study. It was expected that the relative concentration of volatiles would remain the same on both sides of the membrane; however, selective removal of nitroglycerin by some membranes was observed. Synthetic membranes with larger pore sizes showed no alteration in the vapor composition. Both synthetic and glass fiber membranes did not show a significant change in relative concentration of the other volatile compound in dynamite, i.e., EGDN. Out of all the membranes tested, three synthetic membranes and four glass fiber membranes showed selective alteration in odor availability of nitroglycerin in dynamite. For training purposes, membranes that do not alter the vapor composition should be used in the training aid.
Apart from high sensitivity and selectivity of surface-enhanced Raman scattering (SERS)-based trace explosive detection, efficient sampling of explosive residue from real world surfaces is very ...important for homeland security applications. Herein, we demonstrate an entirely new SERS nanosensor fabrication approach. The SERS nanosensor was prepared by self-assembling chemically synthesized gold triangular nanoprisms (Au TNPs), which we show display strong electromagnetic field enhancements at the sharp tips and edges, onto a pressure-sensitive flexible adhesive film. Our SERS nanosensor provides excellent SERS activity (enhancement factor = ∼6.0 × 106) and limit of detection (as low as 56 parts-per-quadrillions) with high selectivity by chemometric analyses among three commonly military high explosives (TNT, RDX, and PETN). Furthermore, the SERS nanosensors present excellent reproducibility (<4.0% relative standard deviation at 1.0 μM concentration) and unprecedentedly high stability with a "shelf life" of at least 5 months. Finally, TNT and PETN were analyzed and quantified by transferring solid explosive residues from fingerprints left on solid surfaces to the SERS nanosensor. Taken together, the demonstrated sensitivity, selectivity, and reliability of the measurements as well as with the excellent shelf life of our SERS nanosensors obviate the need for complicated sample processing steps required for other analytical techniques, and thus these nanosensors have tremendous potential not only in the field of measurement science but also for homeland security applications to combat acts of terror and military threats.
Surface-enhanced Raman scattering (SERS) is an ultrasensitive analytical technique, which is capable of providing high specificity; thus, it can be used for toxicological drug assay (detection and ...quantification). However, SERS-based drug analysis directly in human biofluids requires mitigation of fouling and nonspecificity effects that commonly appeared from unwanted adsorption of endogenous biomolecules present in biofluids (e.g., blood plasma and serum) onto the SERS substrate. Here, we report a bottom-up fabrication strategy to prepare ultrasensitive SERS substrates, first, by functionalizing chemically synthesized gold triangular nanoprisms (Au TNPs) with poly(ethylene glycol)-thiolate in the solid state to avoid protein fouling and second, by generating flexible plasmonic patches to enhance SERS sensitivity via the formation of high-intensity electromagnetic hot spots. Poly(ethylene glycol)-thiolate-functionalized Au TNPs in the form of flexible plasmonic patches show a twofold-improved signal-to-noise ratio in comparison to triethylamine (TEA)-passivated Au TNPs. Furthermore, the plasmonic patch displays a SERS enhancement factor of 4.5 ×107. Utilizing the Langmuir adsorption model, we determine the adsorption constant of drugs for two different surface ligands and observe that the drug molecules display stronger affinity for poly(ethylene glycol) ligands than TEA. Our density functional theory calculations unequivocally support the interaction between drug molecules and poly(ethylene glycol) moieties. Furthermore, the universality of the plasmonic patch for SERS-based drug detection is demonstrated for cocaine, JWH-018, and opioids (fentanyl, despropionyl fentanyl, and heroin) and binary mixture (trace amount of fentanyl in heroin) analyses. We demonstrate the applicability of flexible plasmonic patches for the selective assay of fentanyl at picogram/milliliter concentration levels from drug-of-abuse patients’ blood plasma. The fentanyl concentration calculated in the patients’ blood plasma from SERS analysis is in excellent agreement with the values determined using the paper spray ionization mass spectrometry technique. We believe that the flexible plasmonic patch fabrication strategy would be widely applicable to any plasmonic nanostructure for SERS-based chemical sensing for clinical toxicology and therapeutic drug monitoring.
The nitro functional group (NO2) features strongly in compounds such as explosives, pharmaceuticals, and fragrances. However, its gas phase absorbance characteristics in the vacuum UV region ...(120–200 nm) have not been systematically studied. Gas chromatography/vacuum UV spectroscopy (GC/VUV) was utilized to study the gas phase VUV spectra of various nitrated compounds (e.g., nitrate esters (-R-O-NO2), nitramines (R-N-NO2), nitroaromatics (Ar-NO2), and nitroalkanes (R-NO2)). The nitro absorption maximum appeared over a wide range (170–270 nm) and its wavelength and intensity were highly dependent upon the structure of the rest of the molecule. For example, the nitroalkanes exhibited a trend in that the ratio of the relative absorption intensity between these two absorption features between the alkyl group (<150 nm) and the nitro group (200 nm) increases as the molecular weight increases. It was observed that the addition of multiple nitro functional groups on benzene or toluene resulted in an increase in intensity and blue shift from approximately 240 nm–210 nm. Nitrate esters exhibited an absorption between 170 nm and 210 nm and absorbance increased with increasing nitrogen content. The relative diversity of the spectra obtained was analyzed by Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). These calculations revealed that the spectra of all the compounds analyzed could be reliably differentiated without any misclassifications.
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•Nitro functional group absorption characterized by GC/VUV.•Absorption maxima for nitro group ranged between 170 mn and 270 nm.•Wavelength and intensity were highly dependent upon the molecular structure.•Spectra studied by PCA and LDA reliably differentiated without misclassifications.
The storage and use of explosives is regulated at the state and federal level, with a particular focus on physical security and rigorous accounting of the explosive inventory. For those working with ...explosives for the training and testing of explosive‐detecting canines, cross‐contamination is an important concern. Hence, explosives intended for use with canine teams must be placed into secondary storage containers that are new, clean, and airtight. A variety of containers meet these requirements and include screw‐top glass jars (e.g., mason jars). However, an additional need from the explosive‐detecting canine community is secondary containers that can also be used as training aids whereby the volatiles emitted by explosives are emitted in a predictable and stable manner. Currently, a generally accepted method for the storage of explosives and controlled emission of explosive vapor for canine detection does not exist. Ideally, such containers should allow odor to escape from the training aid but block external contaminates such as particulates or other volatiles. One method in use places the explosive inside a permeable cotton bag when in use for training and then stores the cotton bag inside an impermeable nylon bag for long‐term storage. This paper describes the testing of an odor permeable membrane device (OPMD) as a new way to store and deploy training aids. We measured the evaporation rate and flux of various liquid explosives and volatile compounds that have been identified in the headspace of actual explosives. OPMDs were used in addition to traditional storage containers to monitor the contamination and degradation of 14 explosives used as canine training aids. Explosives were stored individually using traditional storage bags or inside an OPMD at two locations, one of which actively used the training aids. Samples from each storage type at both locations were collected at 0, 3, 6, and 9 months and analyzed using Fourier Transform Infrared (FTIR) Spectroscopy and Gas Chromatography–Mass Spectrometry (GC–MS) with Solid‐Phase Microextraction (SPME). FTIR analyses showed no signs of degradation. GC–MS identified cross‐contamination from ethylene glycol dinitrate (EGDN) and/or 2,3‐dimethyl‐2,3‐dinitrobutane (DMNB) across almost all samples regardless of storage condition. The contamination was found to be higher among training aids that were stored in traditional ways and that were in active use by canine teams.
Analysis of nitrate ester explosives (e.g., nitroglycerine) using gas chromatography–vacuum ultraviolet spectroscopy (GC–VUV) results in their thermal decomposition into nitric oxide, water, carbon ...monoxide, oxygen, and formaldehyde. These decomposition products exhibit highly structured spectra in the VUV that is not seen in larger molecules. Computational analysis using time-dependent density functional theory (TDDFT) was utilized to investigate the excited states and vibronic transitions of these decomposition products. The experimental and computational results are compared with those in previous literature using synchrotron spectroscopy, electron energy loss spectroscopy (EELS), photoabsorption spectroscopy, and other computational excited state methods. It was determined that a benchtop GC–VUV detector gives comparable results to those previously reported, and TDDFT could predict vibronic spacing and model molecular orbital diagrams.
Gas chromatography/mass spectrometry (GC/MS) is a "workhorse" instrument for chemical analysis, but it can be limited in its ability to differentiate structurally similar compounds. The coupling of ...GC to vacuum ultraviolet (VUV) spectroscopy is a recently developed technique with the potential for increased detection specificity. To date, GC/VUV has been demonstrated in the analysis of volatile organic compounds, petroleum products, aroma compounds, pharmaceuticals, illegal drugs, and lipids. This paper is the first to report on the utility of GC/VUV for explosives analysis in general, and the first to report on thermal degradation within the VUV cell and its analytical utility. The general figures of merit and performance of GC/VUV were evaluated with authentic standards of nitrate ester explosives (e.g., nitroglycerine (NG), ethylene glycol dinitrate (EGDN), pentaerythritol tetranitrate (PETN), and erythritol tetranitrate (ETN)). In addition, the explosive analytes were thermally degraded in the VUV cell, yielding reproducible, complex and characteristic mixtures of gas phase products (e.g., nitric oxide, carbon monoxide, and formaldehyde). The relative amounts of the degradation products were estimated via spectral subtraction of library spectra. Lastly, GC/VUV was used to analyze milligram quantities of intact and burned samples of double-base smokeless powders containing nitroglycerine, diphenylamine, ethyl centralite, and dibutylphthalate
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•Coupling gas chromatography to vacuum UV spectroscopy can identify explosives at part-per-million levels.•Increased flow cell temperatures resulted in thermal degradation of the explosives into reproducible and complex mixtures of gaseous products such as nitric oxide, carbon monoxide and formaldehyde.•The resultant VUV spectra are highly structured and therefore specific, differentiating nitrate ester explosives that yield identical EI mass spectra.
Gas Chromatography-Vacuum UV Spectroscopy (GC-VUV) has seen increased attention in many areas, however, a statistical optimization of VUV method parameters has not been published. This article ...presents the first statistical optimization of parameters influencing analytes such as cocaine in the VUV flow-cell. Flow-cell temperature, make-up gas pressure, and carrier gas flow rate from the GC were examined and optimized for the detection of controlled substances. The accuracy, precision, linearity, and optimized detection limits for drugs such as cocaine (98.5%, 1.2%, 0.9998, 1.5 ng), heroin (99.3%, 0.94%, 0.9998, 2.0 ng), and fentanyl (98.5%, 1.7%, 0.9752, 9.7 ng) are reported. In general, the limits of detection for cocaine, heroin, fentanyl, and methamphetamine after optimization were comparable to gas chromatography-mass spectrometry (GC-MS) in “scan mode”, which had detection limits of 1.1–38 ng on column. The VUV absorption spectra of cocaine, PCP, lorazepam, and HU-210 are also reported. And three samples of “real world” cocaine are analyzed to demonstrate applicability to forensic drug analysis.
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•Four spectra of drugs of abuse are reported for the first time.•A systematic optimization of crucial GC-VUV parameters was performed.•“Real World” performance is illustrated through analysis of “street” cocaine samples.
The detection of explosives and explosive devices based on the volatile compounds they emit is a long‐standing tool for law enforcement and physical security. Toward that end, solid‐phase ...microextraction (SPME) combined with gas chromatography–mass spectrometry (GC–MS) has become a crucial analytical tool for the identification of volatiles emitted by explosives. Previous SPME studies have identified many volatile compounds emitted by common explosive formulations that serve as the main charge in explosive devices. However, limited research has been conducted on initiators like fuses, detonating cords, and boosters. In this study, a variety of SPME fiber coatings (i.e., polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), divinylbenzene/carboxin/polydimethylsiloxane (DVB/CAR/PDMS), and carboxin/polydimethylsiloxane (CAR/PDMS)) were employed for the extraction and analysis of volatiles from Composition C‐4 (cyclohexanone, 2‐ethyl‐1‐hexanol, and 2,3‐dimethyl‐2,3‐dinitrobutane (DMNB)) and Red Dot double‐base smokeless powder (nitroglycerine, phenylamine). The results revealed that a PDMS/DVB fiber was optimal. Then, an assortment of explosive items (i.e., detonation cord, safety fuse, slip‐on booster, and shape charge) were analyzed with a PDMS/DVB fiber. A variety of volatile compounds were identified, including plasticizers (tributyl acetyl citrate, N‐butylbenzenesulfonamide), taggants (DMNB), and degradation products (2‐ethyl‐1‐hexanol).
Gas chromatography/vacuum UV spectroscopy (GC/VUV) was utilized to study various explosives and pharmaceuticals in the nitrate ester and nitramine structural classes. In addition to generating ...specific VUV spectra for each compound, VUV was used to indicate the onset of thermal decomposition based upon the appearance of break-down products such as nitric oxide, carbon monoxide, formaldehyde, water, and molecular oxygen. The effect of temperature on decomposition could be fit to a logistical function where the fraction of intact compound remaining decreased as the transfer line/flow cell temperature was increased from 200 °C to 300 °C. Utilizing this relationship, the decomposition temperatures for the nitrate ester and nitramine compounds were determined to range between 244 °C and 277 °C. It was also discovered that the decomposition temperature was dependent on the GC carrier gas flow rate and, therefore, the residence time of the compounds in the transfer line/flow cell. For example, the measured decomposition temperature of nitroglycerine ranged from 222 °C to 253 °C across four flow rates. Tracking the appearance/disappearance of decomposition products across this temperature range indicated that NO, CO, and H2CO are final decomposition products while O2 and H2O are intermediate products. The decomposition temperatures for all explosives were highly correlated to similar decomposition measurements taken by differential scanning calorimetry (DSC) (r = 0.91) and thermal gravimetric analysis (TGA) (r = 0.90–0.98). In addition, the decomposition temperatures for all explosives were negatively correlated to the heat of explosion at constant volume (r = −0.68) and strongly positively correlated to the oxygen balance (r = 0.92).
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•Analysis via gas chromatography/vacuum ultraviolet spectroscopy.•Nitrate esters and nitramines thermally decompose in transfer line/flow cell.•Thermodynamic processes and properties can be determined.•Decomposition temperatures dependent on the residence time in transfer line/flow cell.•Decomposition temperatures highly correlated to thermochemical measurements.
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