Methyl Centralite Research Articles

Evaluation of handheld Raman spectrometers for the detection of intact explosives

The detection of intact explosives in the field provides a unique challenge for investigators, considering the sensitive and dangerous nature of these samples. Handheld Raman instruments have grown in popularity for the analysis of unknown samples in the field, combining speed of data collection and reliability with a size that allows for the instruments to be field portable. Handheld Raman instruments are used commonly in the field, and yet there is very little research on the detection capabilities of these instruments, specifically for explosive compounds. The present study aimed to evaluate the detection capabilities of two handheld Raman spectrometers, the Rigaku ResQ-CQL and the Field Forensics HandyRam™, using explosives analytical standards, including 2,4,6-trinitrotoluene (TNT), nitromethane (NM), ammonium nitrate (AN) and smokeless powder components such as diphenylamine (DPA), ethyl centralite (EC), and methyl centralite (MC). The spectrometers were evaluated on their sensitivity, the repeatability of the data, and the performance of the internal library when available. In addition, an interference study with glass and plastic containers was also performed. Finally, authentic intact explosive samples, including TNT flakes, a mixture of ammonium nitrate and fuel oil (ANFO), smokeless powder and nitromethane were analyzed to evaluate the developed method and test the detection capabilities of the spectrometers with authentic samples. Spectra were reproducible for all the analytes across both instruments, with regards to the peak location and the intensity. Spectra obtained with the Rigaku ResQ-CQL displayed better resolution for all analytes, including the authentic samples. In addition, its wider scan range allowed for the detection of more detailed peaks below 400 cm−1. Identifying the detection capabilities of these handheld instruments can therefore help guide investigators on how to best utilize them in the field.

Isothermal Kinetic Study and Shelf-Life Prediction of Triple Base Propellant Using Vacuum Stability Test in Combination with HPLC and GPC

ABSTRACT In this study, isothermal decomposition kinetic of a triple-base propellant (TBP) has been investigated by vacuum stability test (VST). The volumes of the evolved gas have been recorded step by step to monitor gas evolution in VST at 80°C, 90°C, 100°C, 110°C, 120°C, and 150°C. This semi-continuous data-recording mode makes it possible to use the Berthelot equation for shelf-life prediction of TBP. Activation energy has been calculated in both model-free and model-fitting methods, and F0/R1 is determined as the best model for thermal decomposition of TBP at VST. High-performance liquid chromatography has been used to determine stabilizer (methyl centralite) content of the TBP at various extents of reactions (α). The critical amount of stabilizer was specified at 2% α. Arrhenius average temperatures have been calculated at various climate categories and used as actual storage temperatures. Molecular weight (Mw) reductions of nitrocellulose were determined by gel permeation chromatography during aging. According to the results, the shelf-life of TBP has been estimated using the Berthelot equation at 2% α in various climate categories. Shelf-life of studied TBP differs from 14 to about 36 (years) in extremely hot dry (A1) to intermediate (A3) climate categories.

Detection of organic gunshot residues from human hands using direct sample analysis‐time of flight‐mass spectrometry

AbstractThe organic gunshot residues (OGSRs), specifically methyl centralite (MC; 1,3‐dimethyl‐1,3‐diphenylurea), ethyl centralite (EC; 1,3‐diethyl‐1,3‐diphenylurea), 2,4‐DNT (2,4‐dinitrotoluene), and TNT (trinitrotoluene), are characteristic compounds for which forensic analysts test determining if a person has discharged a firearm. A set of 200 samples from 50 shooters were collected as part of the validation study. Pistol 9 mm and special revolver .38 were fired at indoor and outdoor shooting ranges. The development of a methodology based on direct analysis of samples‐time of flight‐mass spectrometry (DSA‐TOF‐MS) made it possible to identify the main components of organic shot residues, which gave the possibility to introduce a new method of analysis of shot residues in the Chilean supply area. The DSA‐TOF‐MS provided extensive information on the composition of the shot residues: MC, EC, 2,4‐DNT, and TNT. Samples taken from the trigger hands required minimal sample preparation that reduced analyses time. With the implementation of new alternative analytical methodologies, a great step would be taken in the analysis of OGSRs, because now there is no such technique for its analysis in Chile, and the results would also complement the existing inorganic elemental analyses generated during a gunshot.

Effect of ageing on the combustion of single base propellants

This paper shows how the combustion properties of single base nitrocellulose propellants are affected by degradation by ageing. A single base gunpowder sample containing methyl centralite and ethyl centralite as stabilizers was artificially aged by 10, 20 and 25 years. Closed vessel experiments were performed to evaluate the burning rate, the dynamic vivacity, the maximum pressure, the force, and the covolume of the gases produced. The propellant degradation was characterized by the Bergmann-Junk test, heat flow calorimetry test (HFC), high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC). Gel permeation chromatography was especially useful to describe the degradation process. The results found for the burning rate suggest the existence of two phases during ageing: intensification and passivation. The intensification phase occurs while the propellant samples maintain the chemical stability and the passivation phase was observed for the unstable samples.

Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives.

Analysis of smokeless powders is of interest from forensics and security perspectives. This article reports the detection of smokeless powder organic additives (in their pre-detonation condition), namely the stabiliser diphenylamine and its derivatives 2-nitrodiphenylamine and 4-nitrodiphenylamine, and the additives (used both as stabilisers and plasticisers) methyl centralite and ethyl centralite, by means of swab sampling followed by thermal desorption and direct injection soft chemical ionisation-mass spectrometry. Investigations on the product ions resulting from the reactions of the reagent ions H3O+ and O2+ with additives as a function of reduced electric field are reported. The method was comprehensively evaluated in terms of linearity, sensitivity and precision. For H3O+, the limits of detection (LoD) are in the range of 41-88pg of additive, for which the accuracy varied between 1.5 and 3.2%, precision varied between 3.7 and 7.3% and linearity showed R2 ≥ 0.9991. For O2+, LoD are in the range of 72 to 1.4ng, with an accuracy of between 2.8 and 4.9% and a precision between 4.5 and 8.6% and R2 ≥ 0.9914. The validated methodology was applied to the analysis of commercial pre-blast gun powders from different manufacturers. Graphical Abstract.

A forensic investigation on the persistence of organic gunshot residues

Gunshot residues (GSR) are a potential form of forensic traces in firearm-related events. In most forensic laboratories, GSR analyses focus on the detection and characterisation of the inorganic components (IGSR), which are mainly particles containing mixtures of lead, barium and antimony originating from the primer. The increasing prevalence of heavy metal-free ammunition challenges the current protocols used for IGSR analysis. To provide complementary information to IGSR particles, the current study concentrated on the organic components (OGSR) arising from the combustion of the propellant. The study focused on four compounds well-known as being part of OGSR: ethylcentralite (EC), methylcentralite (MC), diphenylamine (DPA), N-nitrosodiphenylamine (N-nDPA). This study assessed the retention of these OGSR traces on a shooter’s hands. The overall project aim was to provide appropriate information regarding OGSR persistence, which can be suitable to be integrated into the interpretation framework of OGSR as recommended by the recent ENFSI Guideline for Evaluative Reporting in Forensic Science. The persistence was studied through several intervals ranging from immediately after discharge to four hours and two ammunition calibres were chosen: .40 S&W calibre, used by the NSW Police Force; and .357 Magnum, which is frequently encountered in Australian casework. This study successfully detected the compounds of interest up to four hours after discharge. The trends displayed a large decrease in the amount detected during the first hour. A large variability was also observed due to numerous factors involved in the production, deposition and collection of OGSR.

The coupling of capillary microextraction of volatiles (CMV) dynamic air sampling device with DART-MS analysis for the detection of gunshot residues

A novel apparatus interfacing capillary microextraction of volatiles (CMV) and direct analysis in real time mass spectrometry (DART-MS) was evaluated for the trace detection and characterization of organic compounds found in smokeless powders and consequently in gunshot residues (GSR). Target analytes included nitroglycerin (NG), diphenylamine (DPA), ethyl centralite (EC), 2,4-dinitrotoluenes (2,4-DNT), methyl centralite (MC), 2,4,6-trinitrotoluene (2,4,6-TNT) and derivatives of DPA generated from the degradation of the energetic material such as 4-nitrosodiphenylamine (4-NODPA), 2-nitrodiphenylamine (2-NDPA) and 4-nitrodiphenylamine (4-NDPA). The results from CMV-DART-MS were compared to the previously reported CMV-GC–MS method through the application of an efficient and calibrated vapor source based on an inert pre-heated GC split/splitless injector port, to simulate field sampling of GSR in the air surrounding a person’s hands. It was found that both DART-MS and GC–MS could be used in succession to detect a suite of compounds at 15 ng sampled vapor within 2.5 L of air to provide more comprehensive characterization of a sample. Overall, a method was developed for the analysis of compounds associated with GSR applying fast, dynamic air sampling (2–5 min) using the CMV device coupled for the first time to DART-MS for fast analysis (∼1 min), compared to GC–MS results under the same sampling conditions of ng quantities of the target analytes of interest.

Swab touch spray mass spectrometry for rapid analysis of organic gunshot residue from human hand and various surfaces using commercial and fieldable mass spectrometry systems

Organic gunshot residues, specifically methyl centralite (1,3-dimethyl-1,3-diphenylurea) and ethyl centralite (1,3-diethyl-1,3-diphenylurea), are characteristic compounds for which forensic analysts test when determining if an individual has discharged a firearm. These distinctive compounds have long been analyzed by several instrumental techniques, many of which involve extensive sample preparation or have lengthy analysis times. Presented here is an ambient ionization method that requires no sample preparation, offers real-time analysis, and can be paired with a portable ion trap mass spectrometer for in-situ analysis. Swab touch spray ionization utilizes a rayon-tipped swab that has an aluminum wire handle which can simply be swabbed over the area of interest. After contacting the hands of the shooter, or other surfaces, the swab simply has solvent applied to the rayon tip and a high voltage applied to the aluminum handle. This process generates ions that the mass spectrometer will use to determine if the organic gunshot residues are present. Mass spectrometry allows for the direct confirmation of organic gunshot residue on suspects hands, confirmed through tandem mass spectrometry. Additional benefits of swab touch spray ionization are that the swabs are commercially available, they are sterile, and they are individually packaged to prevent contamination. The swabs are also forensically feasible because they are sealed prior to delivery by the vendor with a tamper-proof label. Here we have shown that this ambient ionization method allows for the direct swabbing of suspected shooters hands for trace residues and confirm the presence of the two organic gunshot residues investigated.

Identification of polymers and organic gunshot residue in evidence from 3D-printed firearms using DART-mass spectrometry: A feasibility study

Rapid advances in 3D-printing technology have created an emerging class of firearms. As the movement to self-manufacture firearms with 3D-printing grows, it is reasonable to assume that they will be increasingly used in crimes. Here, we test-fired gun barrels made with acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyethylene terephthalate (PETG), chlorinated polyethylene (CPE), and nylon. The resulting cartridge cases, bullets, and gunshot residue (GSR) were examined by direct analysis in real time – mass spectrometry (DART-MS). High-resolution mass spectra detected polymer from the gun barrel on bullets and cartridge casings for a 0.38 special caliber gun and, to a lesser extent, for a 0.22 caliber 3D-printed gun. Particles of plastic were identified in some GSR samples collected from clothing used as a backstop for test-fires. DART-MS also readily detected signature organic GSR compounds, including methyl centralite, ethyl centralite, diphenylamine, and nitrocellulose, on recovered bullets, cartridge cases, and in extracts of SEM stubs used to collect GSR from the clothing. Overall, this study demonstrates that analysis of firearm trace evidence using DART-MS deserves more attention, and that the technique may be particularly useful for investigating crimes involving 3D-printed guns.

Classification of Gunshot Residue Using Laser Electrospray Mass Spectrometry and Offline Multivariate Statistical Analysis.

Nonresonant laser vaporization combined with high-resolution electrospray time-of-flight mass spectrometry enables analysis of a casing after discharge of a firearm revealing organic signature molecules including methyl centralite (MC), diphenylamine (DPA), N-nitrosodiphenylamine (N-NO-DPA), 4-nitrodiphenylamine (4-NDPA), a DPA adduct, and multiple unidentified features not observed in previous mass spectral measurements. Collision-induced dissociation measurements of unknown GSR signature ions reveals inorganic barium and derivatives BaOH, BaOHCH3, BaCH3COO remaining from the primer. Both hydrophilic and hydrophobic signatures are detected using water-methanol electrospray solution. Offline principal component analysis and discrimination of the laser electrospray mass spectral (LEMS) measurements resulted in perfect classification of the gun shot residue with respect to the manufacturer. Principal component analysis of recycled and reloaded casings resulted in classification of the penultimate manufacturer with an accuracy of 89%.

Microextraction of methyl and ethyl centralites using an alkanol-based nanostructured solvent followed by high-performance liquid chromatography

A new, efficient and environmentally friendly method was developed for the analysis of methyl centralite (MC) and ethyl centralite (EC) in propellant using nanostructured supramolecular solvent microextraction. Several conditions affecting extraction efficiency such as the concentration of major components of the nanostructured supramolecular assembly (tetrahydrofuran and alkanol), alkanol type, solvent pH, and extraction time were investigated and optimized as well. High extraction efficiency of analytes was resulted from different types of interaction provided by the supramolecular assembly (e.g., hydrophobic and hydrogen bonds) and the high number of solubilization sites it contains. Besides simplicity and high efficiency, low-cost, environment-friendly, the system setup was implemented using conventional laboratory equipment. Under the optimal conditions, the detection limits of MC and EC in propellant samples were reported 0.007 and 0.010 mg g−1, respectively. Linear dynamic range of MC and EC is 0.04–10.00 mg g−1 with coefficient of determination (R2) of 0.9982 and 0.9997, respectively. The relative standard deviations under intra-day and inter-day conditions varied within the intervals 7.2–10.3 % and 7.6–11.2 %, respectively. Also, recoveries in samples ranged between about 89.5 and 97.3 %.

Application of different standard loading approaches during solid phase microextraction for forensic analysis of single particle smokeless powders

The technique of solid phase microextraction incorporates sampling, isolation and enrichment into a single sample preparation step, making it useful for forensic applications such as the analysis of gunpowder present at trace levels. In this study, three standard loading approaches for the analysis of compounds in smokeless powder – namely the direct headspace extraction of pure standard compounds, the syringe-fibre transfer and the in-vial standard loading approaches – were evaluated. The in-vial standard loading approach was found to be the most suitable method for both the standard curve preparation and sample analysis. Method specificity, linearity, precision, accuracy, recovery, method detection limit and the limit of quantitation were investigated for its intended purpose through the examination of common stabilisers and additives in smokeless powders, namely naphthalene, 2,6-dinitrotoluene, 2,4-dinitrotoluene, diphenylamine, N,N-diphenylformamide, methyl centralite and ethyl centralite by the gas chromatography-flame ionisation detection technique. Examination of four ammunition types of 9 mm calibre enabled their differentiation among the respective smokeless powder samples through comparison of the abundance of selected compounds.

Analysis of ethyl and methyl centralite vibrational spectra for mapping organic gunshot residues.

Detection of ethyl and methyl centralites in gunshot residues is important in forensic science due to their limited contamination from environmental sources compared to other organic residues. However, the vibrational frequencies of centralites are little explored and their frequency assignments are incomplete. Herein, we investigated vibrational frequencies of centralites based on Density functional theory (DFT) to understand their vibrations. The simulated frequencies exhibit excellent agreement with the experimental data, and the detailed assignments are comprehensively elaborated. We also demonstrate that centralite particles could be detected through Raman imaging based on their fingerprints. This work is very important for the further vibrational studies in detecting and tracing centralites in gunshot residues.

DSC measurement and prediction of phase diagrams for binary mixtures of energetic materials’ stabilizers

This study reports the investigation of four binary mixtures of diphenylamine (1)+N-ethyl-4-nitroaniline (2), ethyl centralite (1)+N-ethyl-4-nitroaniline (2), methyl centralite (1)+N-ethyl-4-nitroaniline (2) and N-(2-acetoxyethyl)-p-nitroaniline (1)+N-ethyl-4-nitroaniline (2). The liquidus and solidus equilibrium temperatures determined by differential scanning calorimeter (DSC) were used to construct the corresponding solid–liquid phase diagrams. On the basis of the DSC results, simple eutectic behaviours for four systems were observed. The experimental results were correlated by means of Wilson and UNIQUAC equations.The root-mean-square deviations of the solubility temperatures for all measured data vary from 0.80 to 4.05K and depend on the particular model used. The best solubility correlation was obtained with the UNIQUAC model.

Classification of Smokeless Powders Using Laser Electrospray Mass Spectrometry and Offline Multivariate Statistical Analysis

A direct, sensitive, and rapid method for the detection of smokeless powder components, from five different types of ammunition, is demonstrated using laser electrospray mass spectrometry (LEMS). Common components found in powder, such as ethyl centralite, methyl centralite, dibutyl phthalate, and dimethyl phthalate, are detected under atmospheric conditions without additional sample preparation. LEMS analysis of the powders revealed several new mass spectral features that have not been identified previously. Offline principal component analysis and discrimination of the LEMS mass spectral measurements resulted in perfect classification of the smokeless powder with respect to manufacturer.

Solid–liquid phase equilibria for binary mixtures of propellant’s stabilizers

Solid–liquid equilibria for three binary mixtures of N-(2-acetoxyethyl)-p-nitroaniline (1) + 2-nitrodiphenylamine (2), N-(2-acetoxyethyl)-p-nitroaniline (1) + ethyl centralite (2) and N-(2-acetoxyethyl)-p-nitroaniline (1) + methyl centralite (2) have been determined experimentally using differential scanning calorimeter (DSC). Simple eutectic behaviours for these systems have been observed. The experimental results have been correlated by means of NRTL and UNIQUAC equations. The root-mean-square deviations of the solubility temperatures for all measured data vary from 0.61 to 3.32 K and depend on the particular model used. The best solubility correlation has been obtained with the UNIQUAC model.

Study on the influence of ageing on chemical and mechanical properties of N,N′-dimethyl-N,N′-diphenylcarbamide stabilized propellants

Double-base propellants undergo chemical, physical and mechanical changes upon ageing, leading to changes in ballistic performance and presenting explosive hazards. This report studies the variation of chemical and mechanical properties of aged N,N′-dimethyl-N,N′-diphenylcarbamide (methyl centralite) stabilized propellants in order to simulate and evaluate the natural ageing throughout the artificial one. Therefore, a comparative study of stabilizer depletion, plasticizers content, heat of combustion and mechanical properties such as storage modulus, loss modulus and damping of naturally and artificially aged propellants has been carried out by the following techniques: high-performance liquid chromatography (HPLC), thermogravimetric analyzer (TG), calorimeter of combustion and dynamic mechanical analyzer (DMA), respectively. The results obtained show that all properties are closely connected. In addition, the determination of stabilizer depletion, plasticizers evaporation, decrease of heat of combustion and mechanical properties are very useful for a better understanding of the decomposition and ageing behaviour of propellants. The HPLC investigation of stabilizer has shown good stability of the propellants. The results obtained for DMA have shown that some considerable changes of the mechanical and viscoelastic properties of the propellants occurred during ageing. These results confirm the results obtained by TG for the reduction of the nitroglycerine amount and the decrease of the heat of combustion.

Screening of gunshot residues using desorption electrospray ionisation–mass spectrometry (DESI–MS)

Several studies have indicated that there are potential environmental sources of particles resembling inorganic primer found in gunshot residues (GSR); as a consequence examiners are reluctant to unambiguously assign the origin of inorganic particles. If organic gunshot residues (OGSR) were found in combination with inorganic particles, the possibility of environmental sources could be potentially eliminated, thereby significantly enhancing the strength of the evidence. Methods have been previously described whereby GSR specimens can be analysed for the presence of OGSR or inorganic GRS (IGSR). However, no methods have been reported that allow the analysis of both OGSR and IGSR on the same specimen. Described in this article is a direct method using desorption electrospray ionisation-mass spectrometry (DESI-MS) for the detection of methyl centralite (MC), ethyl centralite (EC) and diphenylamine (DPA) on adhesive tape GSR stubs typically used for scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) analysis. The optimisation of numerous parameters was conducted using an experimental design. The results indicate that direct analysis of these organic components of GSR is possible although some limitations were also identified. This initial investigation has also indicated that subjecting stubs to DESI analysis does not interfere with subsequent SEM-EDX analysis of primer residues; therefore the technique described herein allows a comprehensive examination of GSR that would be highly probative in the event that both OGSR and IGSR are detected in the same specimen.

Analysis of the headspace composition of smokeless powders using GC–MS, GC-μECD and ion mobility spectrometry

Smokeless powder additives are usually detected from an extraction of post-blast residues or unburned powder particles followed by chromatographic analyses. This work presents the first comprehensive study of the detection of volatile and semi-volatile additives of smokeless powders using solid phase microextraction (SPME) as a sampling and pre-concentration technique. The goal of this study is to generate a list of compounds that can be used as target compounds for the vapor phase detection of smokeless powders. Sixty-five smokeless powders were studied using laboratory-based gas chromatography techniques and a field deployable ion mobility spectrometer (IMS). The detection of diphenylamine, ethyl and methyl centralite, 2,4-dinitrotoluene, diethyl and dibutyl phthalate by IMS is suggested as a method to indicate the presence of smokeless powders. A previously reported SPME-IMS analytical approach facilitates rapid sub-nanogram detection of the vapor phase components of smokeless powders. The analyte mass present in the vapor phase was sufficient for a SPME fiber to extract and concentrate most analytes at amounts above the detection limits of both the GC and the IMS methods. Analysis of 65 different smokeless powder samples revealed that diphenylamine was present in the headspace of 96% of the powders studied. Ethyl centralite was detected in 47% of the powders and 8% of the powders contained methyl centralite. Nitroglycerin was the dominant peak present in the headspace of the double-based powders. Another important headspace component, 2,4-dinitrotoluene, was detected in 44% of the powders comprising both double and single-based powders. Static headspace SPME of small amounts (∼100 mg) of smokeless powder samples for ∼5 min at room temperature resulted in the successful detection of the headspace components, demonstrating the applicability of the technique for field detection of smokeless powders using IMS as a detector.

Measurement and prediction of (solid + liquid) equilibria of gun powder’s and propellant’s stabilizers mixtures

A differential scanning calorimetry (d.s.c.) was used to determine binary (solid + liquid) phase equilibria (SLE) for four binary mixtures, viz. ( n-nitrosodiphenylamine + diphenylamine), (2-nitrodiphenylamine + ethyl centralite), (2,4-dinitro-N-ethylaniline + methyl centralite), and (2,4-diphenylamine + 4,4′-dinitroethylcentralite). These compounds are used as stabilizers in gun powders and propellants. Results obtained with this technique are compared with those correlated by NRTL and ideal models. It was found out that all the systems are simple eutectic systems and deviations between experimental and predicted SLE results were observed.