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Nitrate Ester Derivatization for the Generation of Structurally Informative Ions via Gas Chromatography-Mass Spectrometry
Pentaerythritol tetranitrate (PETN) is a nitrate ester explosive commonly used in commercial detonators. Although its degradation properties have been studied extensively, very little information has been collected on its thermal stability in the molten state due to the fact that its melting point is only ∼20 °C below its onset of decomposition. Furthermore, studies that have been performed on PETN thermal degradation often do not fully characterize or quantify the decomposition products. In this study, we heat PETN to melt temperatures and identify thermal decomposition products, morphology changes, and mass loss by ultrahigh-pressure liquid chromatography coupled to quadrupole time of flight mass spectrometry, scanning electron microscopy, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. For the first time, we quantify several decomposition products using independently prepared standards and establish the resulting melting point depression after the first melt. We also estimate the amount of decomposition relative to sublimation that we measure through gas evolution and evaluate the performance behavior of the molten material in commercial detonator configurations.
A review of energetic materials based on the nitric ester functionality is presented. Examined are materials that are classified as primary explosives, pressable secondary explosives, melt-castable secondary explosives, and rocket- and gun-propellant materials. Disclosed are the molecular structures, physical properties, performances, and sensitivities of the most important legacy nitric esters, as well as the relevant new materials developed within the past several years. Where necessary, discussions of the synthetic protocols to synthesize these materials are also presented.
Desorption electrospray ionization (DESI) is applied to the rapid, in-situ, direct qualitative and quantitative analysis of mixtures of explosives and drugs from a variety of fabrics, including cotton, silk, denim, polyester, rayon, spandex, leather and their blends. The compounds analyzed were explosives: trinitrohexahydro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN) and the drugs of abuse: heroin, cocaine, and methamphetamine. Limits of detection are in the picogram range. DESI analyses were performed without sample preparation and carried out in the presence of common interfering chemical matrices, such as insect repellant, urine, and topical lotions. Spatial and depth profiling was investigated to examine the depth of penetration and lateral resolution. DESI was also used to examine cotton transfer swabs used for travel security sample collection in the screening process. High throughput quantitative analysis of fabric surfaces for targeted analytes is also reported.
Mass spectrometry (MS) techniques are highly prevalent in crime laboratories, particularly those coupled to chromatographic separations like gas chromatography (GC) and liquid chromatography (LC). These methods are considered “gold standard” analytical techniques for forensic analysis and have been extensively validated for producing prosecutorial evidentiary data. However, factors such as growing evidence backlogs and problematic evidence types (e.g., novel psychoactive substance (NPS) classes) have exposed limitations of these stalwart techniques. This critical review serves to delineate the current role of MS methods across the broad sub-disciplines of forensic science, providing insight on how governmental steering committees guide their implementation. Novel, developing techniques that seek to broaden applicability and enhance performance will also be highlighted, from unique modifications to traditional hyphenated MS methods to the newer “ambient” MS techniques that show promise for forensic analysis, but need further validation before incorporation into routine forensic workflows. This review also expounds on how recent improvements to MS instrumental design, scan modes, and data processing could cause a paradigm shift in how the future forensic practitioner collects and processes target evidence.
Erythritol tetranitrate (ETN) was prepared independently by two research groups from the USA and the Netherlands. The partially nitrated impurities present in ETN were studied using liquid chromatography-mass spectrometry to address the ultimate challenge in forensic explosives investigations, i.e., providing chemical and tactical information on the production and origin of the explosive material found at a crime scene. Accurate quantification of the tri-nitrated byproduct erythritol trinitrate (ETriN) was achieved by in-lab production of an ETriN standard and using custom-made standards of the two isomers of ETriN (1,2,3-ETriN and 1,2,4-ETriN). Large differences in levels of ETriN were observed between the two sample sets showing that, even when similar synthesis routes are employed, batches from different production locations can contain different impurity profiles. In one of the sample sets the ratios of the lesser partially nitrated impurities, EDiN and EMN, in the ETN samples could be determined. The impurity profiles enable prediction of post-synthesis work-up steps by reduction of the level of partially nitrated products upon recrystallization. However, impurity analysis does not enable predictions with respect to raw material or synthesis route used. Nonetheless, characteristic impurity profiles obtained can be used in forensic casework to differentiate or link ETN samples. However, forensic interpretation can be complicated by acid catalyzed degradation which can cause changes in impurity levels over time. The high food-grade quality of the erythritol precursor materials did not provide other impurity markers using the LC-MS methods in this study. To expand our framework of chemical attribution a follow-up study will be reported that focuses on stable isotope analysis of ETN and its precursor materials that potentially allow predictions for forensic explosives intelligence.
The idea of this book is to present the up-to-date research results on Nitrate Esters as explosive materials. It covers many aspects including the material structures, nitrating agent, chemical synthesis devices, preparation technology, and applications etc. In particular, this work sheds light on the comprehensive utilization and thorough destruction of the used Nitrate Easters which is crucial for preventing repeated pollution. This is a highly informative and instructive book providing insight for the researchers working on nitrating theory, energetic materials and chemical equipments.
Swab touch spray ionization mass spectrometry, an ambient ionization technique, has been applied to the analysis of six explosives from various surfaces including glass, metal, Teflon, plastic, human hands and three types of gloves (nitrile, vinyl and latex). A swab, attached to a metallic handle, was used to sample explosive residues and acted as the ion source. The explosives, 1,3,5‐trinitro‐1,3,5‐triazinane (RDX), 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX), and 2,2‐bis[(nitrooxy)methyl]propane‐1,3‐diyl dinitrate (PETN) had an absolute limit of detection of 10 ng from all the surfaces except for PETN from the nitrile gloves (limit of detection 100 ng). Sodium perchlorate, 2‐methyl‐1,3,5‐trinitrobenzene (TNT) and tetra‐butylammonium perchlorate had limits of detection of 100 pg, 10 pg, and 1 pg, respectively from all surfaces. This study demonstrates the feasibility of swab touch spray ionization mass spectrometry for detection of a wide array of explosives from a variety of forensically applicable surfaces with disposable, commercial, tamperproof and individually‐wrapped conductive swabs without complicated/lengthy sample preparations or extractions. Analysis of Explosive Residues by Swab Touch Spray Ionization Mass Spectrometry.
A validated solid phase extraction (SPE) cleanup procedure utilizing Bond Elut NEXUS co-polymeric cartridges has been applied to soil and swab samples containing pre- and post-blast residues of nitro-organic explosives. In addition, simulated samples were also processed by SPE to evaluate matrix rejection and interferences. The matrices were extracted with acetone, diluted with deionized water, and processed by SPE. The final extracts were then analyzed by gas chromatography with electron capture detection (GC/ECD) to screen for the compounds of interest, which included ethylene glycol dinitrate (EGDN), dimethyl dinitrobutane (DMDNB), 4-nitrotoluene (4-NT), nitroglycerin (NG), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), pentaerythritol tetra-nitrate (PETN), cyclotrimethylene trinitramine (RDX), 2,4,6-trinitrophenylmethylnitramine (tetryl), cyclotetra-methylene tetranitramine (HMX), erythritol tetranitrate (ETN), and cyclotrimethylene trinitrosoamine (R-salt). The expected explosives were detected in 97% of cases after processing through SPE and analysis by GC/ECD. Approximately one-third of the samples that screened positive by ECD were subjected to confirmation testing by gas or liquid chromatography/mass spectrometry (GC/MS or LC/MS). The results from these matrices were compared to results obtained by syringe filtration. SPE produced equal or better results than syringe filtration in both the ECD screening and MS confirmation tests, including the ability to detect higher signals for more explosives in the post-blast residue samples. The confirmation results also show that all of the expected explosives could be confirmed after processing by SPE, whereas only 83% of them were confirmed after syringe filtration. This study demonstrates the successful application of a validated method to the cleanup of organic explosive residues in complex matrices.
Rationale:
A desired feature in the analysis of explosives is to decrease the time of the entire analysis procedure, including sampling. A recently utilized ambient ionization technique, paper spray ionization (PSI), provides the possibility of combining sampling and ionization. However, an interesting phenomenon that occurs in generating negatively charged ions pose some challenges in applying PSI to explosives analysis. The goal of this work is to investigate the possible solutions for generating explosives ions in negative mode PSI.
Methods:
The analysis of 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) was performed. Several solvent systems with different surface tensions and additives were compared to determine their effect on the ionization of explosives. The solvents tested include tert-butanol, isopropanol, methanol, and acetonitrile. The additives tested were carbon tetrachloride and ammonium nitrate.
Results:
Of the solvents tested, isopropanol yielded the best results. In addition, adding ammonium nitrate to the isopropanol enhanced the analyte signal. Experimentally determined limits of detection (LOD) as low as 0.06 ng for PETN, on paper, were observed with isopropanol and the addition of 0.4 mM ammonium nitrate as the spray solution. In addition, the explosive components of two plastic explosive samples, Composition 4 and Semtex, were successfully analyzed via surface sampling when using the developed method.
Conclusions:
The analysis of explosives using PSI-MS in negative ion mode was achieved. The addition of ammonium nitrate to isopropanol, in general, enhanced the analyte signal and yielded better ionization stability. Real world explosive samples were analyzed, which demonstrates one of the potential applications of PSI-MS analysis.
An ambient mass spectrometry (MS) platform coupling resistive Joule heating thermal desorption (JHTD) and direct analysis in real time (DART) was implemented for the analysis of inorganic nitrite, nitrate, chlorate, and perchlorate salts. The resistive heating component generated discrete and rapid heating ramps and elevated temperatures, up to approximately 400 °C/s and 750 °C, by passing a few amperes of DC current through a nichrome wire. JHTD enhanced the utility and capabilities of traditional DART-MS for the trace detection of previously difficult to detect inorganic compounds. A partial factorial design of experiments (DOE) was implemented for the systematic evaluation of five system parameters. A base set of conditions for JHTD-DART-MS was derived from this evaluation, demonstrating sensitive detection of a range of inorganic oxidizer salts, down to single nanogram levels. DOE also identified JHTD filament current and in-source collision induced dissociation (CID) energy as inducing the greatest effect on system response. Tuning of JHTD current provided a method for controlling the relative degrees of thermal desorption and thermal decomposition. Furthermore, in-source CID provided manipulation of adduct and cluster fragmentation, optimizing the detection of molecular anion species. Finally, the differential thermal desorption nature of the JHTD-DART platform demonstrated efficient desorption and detection of organic and inorganic explosive mixtures, with each desorbing at its respective optimal temperature.
A mixture of explosives was analyzed by gas chromatography (GC) linked to ultraviolet (UV) spectrophotometry that enabled detection in the range of 178-330 nm. The gas-phase UV spectra of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), ethylene glycol dinitrate (EGDN), glycerine trinitrate (NG, nitroglycerine), triacetone triperoxide (TATP), and pentaerythritol tetranitrate (PETN) were successfully recorded. The most interesting aspect of the current application is that it enabled simultaneous detection of both the target analyte and its decomposition products. At suitable elevated temperatures of the transfer line between the GC instrument and the UV detector, a partial decomposition was accomplished. Detection was made in real time and resulted in overlaid spectra of the mother compound and its decomposition product. Hence, the presented approach added another level to the qualitative identification of the explosives in comparison with traditional methods that relies only on the detection of the target analyte. As expected, the decomposition product of EGDN, NG, and PETN was NO, while TATP degraded to acetone. DNT and TNT did not exhibit any decomposition at the temperatures used.
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA ICP-MS) were used for characterization and identification of unique signatures from a series of 18 Composition C-4 plastic explosives. The samples were obtained from various commercial and military sources around the country. Positive and negative ion ToF-SIMS data were acquired directly from C-4 residue on Si surfaces, where the positive ion mass spectra obtained were consistent with the major composition of organic additives, and the negative ion mass spectra were more consistent with explosive content in the C-4 samples. Each series of mass spectra was subjected to Partial Least Squares-Discriminant Analysis (PLS-DA), a multivariate statistical analysis approach which serves to first find the areas of maximum variance within different classes of C-4, and subsequently to classify unknown samples based on correlations between the unknown dataset, and the original dataset (often referred to as a training dataset). This method was able to successfully classify test samples of C-4, though with a limited degree of certainty. The classification accuracy of the method was further improved by integrating the positive and negative ion data using a Bayesian approach. The ToF-SIMS data was combined with a second analytical method, LA ICP-MS, which was used to analyze elemental signatures in the C-4. The integrated data were able to classify test samples with a high degree of certainty. Results indicate that this Bayesian integrated approach constitutes a robust classification method that should be employable even in dirty samples collected in the field.
The molecular characteristics of nitrocelluloses that are used as propellants and have nitrogen contents in the range from 12.2 to 13.44 mol% were characterized through both gel permeation chromatography (GPC) with a refractive index (RI) detector and solution viscometry measurements. The weight-average molecular weights (Mw) and number-average molecular weights (Mn) estimated from the GPC measurements correlated well with the viscosity-average molecular weights obtained from the intrinsic viscosity measurements using an Ubbelohde capillary viscometer for the different nitrogen contents.
GC/MS is used in our laboratory to confirm the identity of explosives in post-explosion debris. The GC/MS analysis of PETN has often been unsuccessful, mainly due to its thermal decomposition under GC conditions. Changing experimental conditions , using a very short (1.5 m) capillary column , solved the probeem. PETN in post-explosion samples was reported to be occasionally accompanied by its degradation products . We have found a similar behaviour of NG in actual post-explosion samples. The TLC plates of these samples contained several Griess — positive spots which corresponded to mono- and dinitrate esters of glycerol. These esters were independently synthesized and characterized . Their analysis was carried out using silylation, GC/EIMS and GC/CIMS. It is suggested that the identification of nitrate esters of pentaerythritol (other than PETN) and glycerol (other than NG) can be used to prove the original presence of PETN and NG in the debris .
Solid phase microextraction and solvent extraction were used with GC/MS to determine the vapor and compositional profile of three samples of Semtex (1A, H, and 10). Semtex is reported to contain PETN and/or RDX, along with plasticizers, binding materials, and fuel oil components. In an effort to differentiate and compare these three variations of Semtex, this report summarizes the headspace and solvent extraction results for each material. Components that can be used to differentiate varieties of Semtex were identified and all three Semtex profiles were distinguished.
This review gives an overview of the developments in the field of analysis of explosives by HPLC for forensic applications. The review covers almost all aspects of analysis such as the analyte's category, matrix involved, technique and conditions used for preconcentration, column and mobile phase used, and subsequent detection in tabular form. This paper covers only organic explosives, e.g., nitroaromatic, nitramine, nitrate esters, peroxide-based explosives and their metabolites and their analysis in various environmental and biological samples like air, water, soil and blood serum.
Pentaerythritol tetranitrate (PETN) and its degradation products are analyzed to discriminate between residues originating from PETN explosions and residues obtained under other circumstances, such as natural degradation on textile, or after handling intact PETN. The degradation products observed in post-explosion samples were identified using liquid chromatography-mass spectrometry as the less-nitrated analogues of PETN: pentaerythritol trinitrate (PETriN), pentaerythritol dinitrate (PEDiN) and pentaerythritol mononitrate (PEMN). Significant levels of these degradation products were observed in post-explosion samples, whereas only very low levels were detected in a variety of intact PETN samples and naturally degraded PETN. No significant degradation was observed after 12 weeks of storage at room temperature and the influence of high relative humidity (90%) was found to be small. Natural degradation was accelerated by storage of small amounts of PETN on different types of textile, resembling the clothing of a suspect, at elevated temperature (333K). This resulted in significant levels of PETN degradation products, but the relative amounts remained much lower than in post-explosion PETN. For PETriN the peak area relative to PETN was 0.014 (SD=0.0051) and 0.39 (SD=0.19) respectively. Based on the peak areas of PETriN, PEDiN and PEMN relative to PETN, it was possible to fully distinguish the post-explosion profiles from the profiles obtained from intact PETN or after (accelerated) natural degradation. Although more data are required to accurately assess the strength of the evidence, this work illustrates that PETN profiling may yield valuable evidence when investigating a possible link between a suspect and post-explosion PETN found on a crime scene. Due to the substantial variation in the degradation pattern between explosion experiments and even between sampling positions in one experiment, the method is not able to distinguish different PETN explosion events.
TLC of post-explosion debris showed that in some cases PETN was accompanied by other compounds which reacted with Griess reagent. The possibility that these compounds could be lower nitrate esters of pentaerythritol (tri-, di- and mononitrate) was examined. Lower nitrate esters were obtained by hydrolysis of PETN and their structures were determined–following separation–by mass spectrometry and NMR. Chromatographic data of these esters matched data of the compounds which accompanied PETN in certain post-explosion cases. The dinitrate and trinitrate esters of pentaerythritol were isolated from post-explosion extracts and their structures confirmed by mass spectrometry and NMR.
It has been found that, with sufficiently high concentrations, simple nitrate esters react with hydrazine at ordinary temperatures in the absence of catalysts. Primary aliphatic nitrates undergo reduction and substitution, yielding nitrogen, nitrous oxide, ammonia, hydrazoic acid, nitrite ion, nitrate ion, alkylated hydrazines, alcohol and traces of aldehyde. High hydrazine concentrations favor the reduction process. A mechanism is proposed for the reduction, based on other known reactions of nitrate esters and on postulated mechanisms for other oxidations of hydrazine. Benzyl nitrate reacts primarily by the substitution process, although a small amount of reduction also occurs with high concentrations of hydrazine. Some α-hydrogen elimination apparently occurs, forming benzaldehyde and nitrous acid. t-Butyl nitrate undergoes β-elimination almost exclusively, giving isobutylene and nitrate ion. Small amounts of substitution products are also obtained, but no nitrogen or nitrogen oxides are formed.
A number of organic nitrate and nitrite esters have been shown to react with lithium aluminum hydride in ether solution to give, after hydrolysis, essentially quantitative yields of the parent alcohol. The other products were nitrous oxide, ammonia and hydrogen. Nitrites produced relatively more nitrous oxide and less ammonia than nitrates. Cellulose nitrates of various degrees of nitration were completely denitrated in tetrahydrofuran. Viscosity measurements indicated extensive degradation of the polymer had occurred.
The polarography and large scale reduction of ethyl and cyclohexyl nitrate were studied. Between pH 3 and 13, a pH-independent reduction wave was obtained and the reduction found to be diffusion controlled. A two-electron reduction mechanism with alcohol and nitrite ion as products was established and found to be consistent with all observations. The polarography of these nitrate esters in the presence of Ce+++, La+++, UO2++ was also studied and the behavior of nitrite ion at the dropping mercury electrode in the presence of uranyl ion was reinvestigated.
The separation and estimation of carbohydrates and related polyhydroxy compounds by gas-liquid chromatography of trimethylsilyl (TMS) derivatives is described. The formation of the TMS derivative, in pyridine containing hexamethyldisilazane and trimethylchlprosilane, occurs very rapidly at room temperature so that analyses can be made within a few minutes. Comparative studies of the reaction product of methyl a-glucopyranoside and authentic methyl (tetra-O-trimethylsilyl )-α-glucOpyranoside indicate that silylation of all free hydroxyl groups occurs and that the yield of TMS derivative is virtually quantitative. Conditions are described for chromatography of a wide variety of carbohydrates from C 2 (glycolaldehyde) to C 24 (stachyose) and related substances such as glycosides, deoxysugars, inositols, hexosamines, and N-acetylneuraminic acid. Most of the studies have been made with a silicone column (SE-52) and a polyester column (polyethylene glycolsuccinate) but separations of the TMS derivatives are possible on other polar and non-polar columns. Iso-thermal conditions are usually employed for separations within a narrow range of molecular weight; separations of more complex mixtures, with components of widely differing molecular weights, may be made by linear temperature-programmed analysis. Excellent separations are generally observed with anomeric pairs as well as configurational isomers within a given class such as pentoses, hexoses, disaccharides, etc. The identity of an unknown sugar may be determined by multiple analyses on a number of liquid phases or, alternatively, by analyses of the parent sugar and various derivatives such as methyl glycoside, alcohol, lactone, oxime, and acetal. In all such cases TMS derivatives are prepared prior to gas chromatography. Comparisons are reported for the compositions of aqueous equilibrium solutions of aldoses, by gas Chromatographic analysis, with those reported by measurements of optical rotation and bromine oxidation. Ih several cases unexpected retention times are interpreted in terms of conformational differences of the sugars.
Rates of thermal decomposition and solvent rate effects have been measured for a series of nitrate esters. The alkoxy radicals formed by homolysis together with some of their further degradation products have been stabilized by hydrogen donation. Internal and external return of nitrogen dioxide have been demonstrated by solvent cage effects and isotope exchange. Radical-stabilizing substituents favor beta-scission. Dinitrates in a 1,5 relationship behave as isolated mononitrates. Dinitrates in a 1,3 or 1,4 relationship exhibit intramolecular reactions. Tertiary nitrate esters in diethyl ether undergo elimination rather than homolysis.
A study was made of the hydrolysis of C14-tagged pentaerythritol tetranitrate (PETN) by 1N HCl in 75% aqueous dioxane. Thin layer chromatography was employed to resolve hydrolysis mixtures into the four nitrate esters and pentaerythritol (PE). Radio scanning was used to locate the compounds. PE, PETN, and PE-trinitrate were identified by comparative chromatography in several solvents and the unavailable mono- and dinitrates of PE were located by their nitrate/carbon ratio. The scanning technique also provided quantitative data which indicated that the four esters of PE have similar rates of hydrolysis.
The analysis of nine explosive compounds by gas chromatography tandem mass spectrometry (GC–MS/MS) using negative chemical ionization (NCI) was performed under two different conditions: first, a conventional GC separation coupled with a standard ion dissociation method in a quadrupole ion trap (QIT) was performed in segmented selected reaction monitoring mode; second, a fast GC separation on a microbore capillary column was combined with a faster method of collisional activation in ion traps wherein fragmentation is deliberately accomplished during the mass acquisition scan. The conventional GC–MS/MS method provided separation times in 10 min with detection limits between 0.8 and 280 pg on column. The fast GC method with dynamic collision-induced dissociation (DCID) offered a confirmatory method for the analysis of high explosives with separation times under 2.5 min and detection limits between 0.5 and 5 pg on column, without any hardware modifications to the instrument. The implementation of DCID in combination with three-times-faster mass scanning allows the acquisition of tandem mass spectra to at least 5 Hz (while averaging three scans per spectrum). Although detection limits for GC-NCI–MS/MS using conventional CID or DCID are not quite on par with LODs achieved by GC-ECD, the combination of NCI with DCID tandem MS leads to detection limits at least comparable, if not superior, to other mass spectrometric methods. Selected reaction monitoring in the negative ionization mode is anticipated to offer the most selective approach to detecting explosives and eliminating potential interferences, which could ultimately lead to the best detection limits for real, contaminated samples.
The characteristics of high-performance liquid chromatographic and gas chromatographic-electron capture assay systems are described for the separation of nitroglycerin from its metabolic and hydrolysis products: 1,2-dinitroglycerin, 1,3-dinitroglycerin, 1-mononitroglycerin and 2-mononitroglycerin. The methods quantitate the amount of parent compound and its major metabolites and were used to measure the rate of acid hydrolysis of nitroglycerin and its dinitro compounds. Assignment of the several peaks in the chromatograms is unequivocal as shown through the use of synthesized metabolites and hydrolysis studies.
The application of surface analytical techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) is explored as a means of differentiating between composition C4 plastic explosives (C-4). Three different C-4 samples including U.S. military grade C-4, commercial C-4 (also from the United States), and C-4 from England (PE-4) were obtained and analyzed using both ToF-SIMS and XPS. ToF-SIMS was able to successfully discriminate between different C-4 samples with the aid of principal component analysis, a multivariate statistical analysis approach often used to reduce the dimensionality of complex data. ToF-SIMS imaging was also used to obtain information about the spatial distribution of the various additives contained within the samples. The results indicated that the samples could potentially be characterized by their 2-D chemical and morphological structure, which varied from sample to sample. XPS analysis also showed significant variation between samples, with changes in the atomic concentrations, as well as changes in the shapes of the high-resolution C 1s and O 1s spectra. These results clearly demonstrate the feasibility of utilizing both ToF-SIMS and XPS as tools for the direct characterization and differentiation of C-4 samples for forensic applications.
Nitrate esters have been known as useful energetic materials since the discovery of nitroglycerin by Ascanio Sobrero in 1846. The development of methods to increase the safety and utility of nitroglycerin by Alfred Nobel led to the revolutionary improvement in the utility of nitroglycerin in explosive applications in the form of dynamite. Since then, many nitrate esters have been prepared and incorporated into military applications such as double-based propellants, detonators and as energetic plasticizers. Nitrate esters have also been shown to have vasodilatory effects in humans and thus have been studied and used for treatments of ailments such as angina. The mechanism of the biological response towards nitrate esters has been elucidated recently. Interestingly, many of the nitrate esters used for military purposes are liquids (ethylene glycol dinitrate, propylene glycol dinitrate, etc). Pentaerythritol tetranitrate (PETN) is one of the only solid nitrate esters, besides nitrocellulose, that is used in any application. Unfortunately, PETN melting point is above 100 {sup o}C, and thus must be pressed as a solid for detonator applications. A more practical material would be a melt-castable explosive, for potential simplification of manufacturing processes. Herein we describe the synthesis of a new energetic nitrate ester (1) that is a solid at ambient temperatures, has a melting point of 85-86 {sup o}C and has the highest density of any known nitrate ester composed only of carbon, hydrogen, nitrogen and oxygen. We also describe the chemical, thermal and sensitivity properties of 1 as well as some preliminary explosive performance data.
The fate of glycerol trinitrate when exposed to microbial attack has been investigated. Contrary to some earlier reports, this compound was readily biodegraded by employing batch or continuous techniques under a variety of cultural conditions. Breakdown of glycerol trinitrate took place stepwise via the dinitrate and mononitrate isomers, with each succeeding step proceeding at a slower rate. After a residence time of 8 to 15 h, none of the glycerol nitrates could be detected in the effluent from a continuous-culture apparatus (chemostat) supplied with an influent containing 30 mg of glycerol trinitrate per liter.
Trimethylsilyl derivatives of α- and β-D-glucose were determined quantitatively, with an internal standard such as terphenyl or triphenylethylene. The results are reproducible to about ±1 per cent.
Method detection limits are determined and compared for analysis of liquid injections of organic explosives and related compounds by gas chromatography-mass spectroscopy utilizing electron impact (EI), negative ion chemical ionization (NICI), and positive ion chemical ionization (PICI) detection methods. Detection limits were rigorously determined for a series of dinitrotoluenes, trinitrotoluene, two nitroester explosives, and one nitramine explosive. The detection limits are lower by NICI than by EI or PICI for all explosives examined, with the exception of RDX. The lowest detection limit for RDX was achieved in the PICI ionization mode. Judicious choice of the appropriate ionization mode can enhance selectivity and significantly lower detection limits. Major ions are reported for each analyte in EI, PICI, and NICI detection modes.
Liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), in the negative-ion mode, was investigated for the analyses of three widely used nitrate ester explosives, pentaerythritol tetranitrate, nitroglycerin and ethylene glycol dinitrate, as well as six additional nitrate esters, using post-column additives. In ESI, ammonium nitrate, sodium nitrite, propionic acid and ammonium chloride promoted formation of characteristic adduct ions of the respective nitrate esters. In APCI, chlorinated agents, dichloromethane, chloroform, carbon tetrachloride and ammonium chloride, were employed, fanning chloride attachment adduct ions. Three forensic samples, Booster DYNO, Semtex and Smokeless Powder, were analyzed to demonstrate the validity of the developed LC-MS methods.
This chapter discusses the sugar nitrates. Nitrates of sugars and their derivatives are colorless compounds, which do not deteriorate on storage at room temperature. Nearly all crystallize readily. Their solubility depends partly on any other substituents present in the molecule, but in general, the introduction of nitrate groups increases the solubility in less polar solvents. Most sugar nitrates are isolated by pouring the reaction solution into water. In many cases, the products solidify and are obtained pure by direct recrystallization from the appropriate solvent. Purification by distillation is not recommended because of the danger of explosion. Chromatography on alumina is outstandingly successful for purifying and separating mixtures of D-glucose nitrates, and derivatives thereof. Although fully nitrated monosaccharides reduce Fehling solution, presumably because of decomposition by the alkaline reagent, there is little evidence suggesting that they mutarotate. No indication of this is found in reports on the physical constants of the D-glucopyranose pentanitrates or the D-galactose pentanitrates.
The fragment ion formation characteristics of the radical anions generated from hexahydro-1,3,5-trinitrotriazine (RDX) and its three nitroso metabolites were studied using GC/MS with negative chemical ionization (NCI) to understand the fragmentation mechanisms responsible for the formation of the most abundant ions observed in their NCI mass spectra. Ab initio and density functional theory calculations were used to calculate relative free energies for different fragment ion structures suggested by the m/z values of the most abundant ions observed in the NCI mass spectra. The NCI mass spectra of the four nitramines are dominated by ions formed by the cleavage of nitrogen-nitrogen and carbon-nitrogen bonds in the atrazine ring. The most abundant anions in the NCI mass spectra of these nitramines have the general formulas C(2)H(4)N(3)O (m/z 86) and C(2)H(4)N(3)O(2) (m/z 102). The analyses of isotope-labeled standards indicate that these two ions are formed by neutral losses that include two exocylic nitrogens and one atrazine ring nitrogen. Our calculations and observations of the nitramine mass spectra suggest that the m/z 86 and m/z 102 ions are formed from either the (M--NO)(-) or (M--NO(2))(-) fragment anions by a single fragmentation reaction producing neutral losses of CH(2)N(2)O or CH(2)N(2)O(2) rather than a set of sequential reactions involving neutral losses of HNO(2) or HNO and HCN.
A solid-phase extraction procedure was developed for the clean-up of forensic samples collected at bombing scenes. Recoveries of common organic explosives from methanolic extracts diluted with water were studied on different hydrophobic sorbents. Polymeric sorbents retained explosive compounds better than octadecyl-bonded silica-based materials. Clean-up efficiency was evaluated with simulated samples prepared from commercial motor oil. Polymeric sorbent with the smallest specific surface area was found to limit the coextraction of matrix components. Performance of the method was confirmed by a reduction of ion suppression in LC/MS analysis.
The action of the grignard reagent on certain nitrate esters
- Helpworth
Characterization and analysis of tetranitrate esters
- J C Oxley
- J L Smith
- J E Brady
- A C Brown
Solution characteristics of nitrocellulose
- Kim