An investigation into artefacts formed during gas chromatography/mass spectrometry analysis of firearms propellant that contains diphenylamine as the stabiliser

Rapid assessment of residual solvent content in the TEGDN dual-base propellants by near-infrared reflectance spectroscopy

Excessive residual solvent (RS) levels in triethyleneglycol dinitrate (TEGDN) dual-base propellants can significantly impair combustion performance. This work aimed to develop a rapid and accurate model for detecting the RS content in the TEGDN dual-base propellants using near-infrared (NIR) spectroscopy in the reflectance mode. The optimal wavelength range for modelling, spanning from 1124.9-1230.2 nm and 1335.5-1527.5 nm, was identified based on absorption peaks characteristic of TEGDN dual-base propellant samples and RS. To enhance the quality of the data, we determined optimal window sizes for pre-processing methods: derivative pre-processing and Savitzky-Golay (S-G) smoothing pre-processing. After evaluating the performance of different pre-treatment methods, we found that the model employing multiple scattering corrections (MSC) in conjunction with first-order derivative (FD) pre-processing demonstrated superior results. The partial least squares (PLS) method was used to build the RS model with an optimal number of factors of 6. For the developed RS model, the root mean square error of calibration (RMSEC) and the root mean square error of cross-validation (RMSECV) were 0.019 and 0.024, respectively. The determination coefficient of calibration (Rc2) and the determination coefficient of cross-validation (Rcv2) were 0.968 and 0.952, respectively. In assessing the validation set using the developed model, we observed a root mean square error of prediction (RMSEP) of 0.025 and a determination coefficient of prediction (Rp2) of 0.958. Importantly, the relative error between the predicted values obtained through the NIR method and the measured values from the reference method consistently remained below 2 % under all circumstances. Consequently, the NIR-based RS model developed in this study offers a rapid and efficient means of detecting RS content in TEGDN dual-base propellants, facilitating judgment regarding the qualification of RS content.

An approach to detecting diphenylamine content and assessing chemical stability of single-base propellants by near-infrared reflectance spectroscopy

Diphenylamine (DPA) as a stabilizer component plays an important role in maintaining the chemical stability of single-base propellants (SBPs). This work investigated the feasibility of rapidly detecting the content of DPA in SBP by near-infrared reflectance spectroscopy (NIRS). The quantitative NIR model was developed by intervals selection, spectral pretreatment and factor number optimization. The optimal spectral intervals were determined to be 1081 nm ∼ 1280 nm and 1378 nm ∼ 1602 nm based on the characteristic spectral peaks of DPA. By comparing the performance of the developed models with different preprocessing methods, the best preprocessing method was standard normal variate transformation (SNV) + de-trending (Dr) + Smoothing. The optimal number of factors was 6 for DPA model. Partial least squares (PLS) regression was used to establish the calibration models of DPA. For the developed model, the determination coefficients of calibration and prediction (R_c², R_p²) were 0.9907 and 0.9884, respectively. The root mean square errors of calibration and prediction (RMSEC, RMSEP) were 0.0310 and 0.0342, respectively. The samples in the prediction set were predicted by the developed model, and the average absolute error of the proposed and reference method was only 0.0265. The developed model can be applied in rapid monitor the content of DPA in SBP. In addition, vieille test have demonstrated that the chemical stability of SBP became worse with the decrease of DPA content. The content of DPA contained in the SBP with qualified chemical stability is not less than 0.8753%. Thus, the developed model can be used to judge whether the chemical stability of SBP is qualified or unqualified.

Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Analysis of Eutectic Bis(2,2-dinitropropyl) Acetal/Formal Degradation Profile: Nontargeted Identification of Antioxidant Derivatives

In the eutectic mixture of bis(2,2-dinitropropyl) acetal (BDNPA) and bis(2,2-dinitropropyl) formal (BDNPF), also known as nitroplasticizer (NP), n-phenyl-β-naphthylamine (PBNA), an antioxidant, is used to improve the long-term storage of NP. PBNA scavenges nitrogen oxides (e.g., NO _x radicals) that are evolved from NP decomposition, hence slowing down the degradation of NP. Yet, little is known about the associated chemical reaction between NP and PBNA. Herein, using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF), we thoroughly characterize nitrated PBNA derivatives with up to five NO₂ moieties in terms of retention time, mass verification, fragmentation pattern, and correlation with NP degradation. The propagation of PBNA nitration is found to depend on the temperature and acidity of the NP system and can be utilized as an indirect, yet reliable, means of determining the extent of NP degradation. At low temperatures (<55 °C), we find that the scavenging efficiency of PBNA is nullified when three NO₂ moieties are added to PBNA. Hence, the dinitro derivative can be used as a reliable indicator for the onset of hydrolytic NP degradation. At elevated temperatures (≥55 °C) and especially in the dry environment, the trace amount of water in the condensed NP (<700 ppm) is essentially removed, which accelerates the production of reactive species (e.g., HONO, HNO₃ and NO _x ). In return, the increased acidity due to HNO₃ formation catalyzes the hydrolysis of NP and PBNA nitro derivatives into 2,2-dinitropropanol (DNPOH) and nitrophenol/dinitrophenol, respectively.

Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry: A Strategy for Optimization, Characterization, and Quantification of Antioxidant Nitro Derivatives

As an antioxidant, N-phenyl-β-naphthylamine (PBNA) inhibits the activity of oxidants, such as NO _x , to prevent the degradation of energetic materials. In the presence of NO _x , nitrated products can be generated in the process potentially. To characterize nitrated PBNA in a nontargeted analysis of complex samples as such, liquid chromatography tandem quadrupole time-of-flight (LC-QTOF), as an excellent analytic technique, is used due to its high resolution and sensitivity. However, a systematic approach of instrumentation optimization, data interpretation, and quantitative determination of products is needed. Through a step-by-step evaluation of the instrumental parameters used in the Q0, Q1, and Q2 compartments of LC-QTOF, optimal ion yields of precursor ions and high-resolution MS² fragmentation spectra at low mass defects were obtained in both negative and positive electrospray ionization modes. Through rationalization of the fragmentation pathways and verification using theoretical masses, the mononitro derivative of PBNA was accurately identified as N-(4-nitrophenyl)-naphthalen-2-amine and further confirmed using a reference standard. Using strict criteria provided by the analytical guidelines (e.g., SANTE), limit of quantitation, limit of detection, and calibration were established for the quantitation of PBNA and nitrated PBNA. From optimization to characterization and subsequent quantification of the mononitro-PBNA derivative, for the first time, the applicability of this strategy is demonstrated in the aged energetic binders.

Magnetic nanoparticle modified electrodes for voltammetric determination of propellant stabiliser diphenylamine

The overall aim of the work was to advance electrochemical devices capable of analysis of forensically relevant residues using rapid electrochemical sensor technology. In order to achieve this, electrochemical detection of the propellant stabiliser diphenylamine (DPA) was achieved via voltammetry with signal enhancement realised in the presence of iron oxide nanoparticle modified transducers. This allowed both mechanistic and analytical evaluation with the aim to achieve the required selectivity and sensitivity for reliable detection. DPA electrochemistry was examined at glassy carbon electrodes in aqueous (3:7 methanol: sodium acetate pH 4.3) electrolyte via potential sweeping, with an irreversible wave at E_p = 0.67 V vs. Ag/AgCl. The diffusion coefficient (D) for the oxidation process was calculated as 1.43 × 10^-6 cm² s^-1 with αn_a = 0.7. DPA electrochemistry in a non aqueous methanol/acetonitrile electrolyte resulted in a D value of 5.47 × 10^-8 cm² s^-1 with αn_a = 0.5. Electrochemical preparation of magnetic iron oxide nanoparticles was achieved via electrooxidation of an iron anode in the presence of an amine surfactant followed by characterisation with SEM/EDX, XRD, FTIR and thermal analysis. A surface confined layer of these magnetic nanoparticles served to positively influence the response to DPA while impeding formation of surface confined oxidation products, with generation of an improved analytical signal - sensitivity 1.13× 10^-3 A cm^-2 mM^-1 relative to bare electrode response (9.80 × 10^-4 A cm^-2 mM^-1) over the range 0.5-50 μM DPA using differential pulse voltammetry, with LOD 3.51 × 10^-6 M and LOQ 1.17 × 10^-5 M. Real sample analysis involved recovery and differential pulse voltammetry of unburnt and burnt gunshot residue with DPA qualitative and quantitative analysis.

An approach for simultaneous monitoring the content of insensitive agent in the double-base oblate spherical propellant by application of near-infrared spectroscope and partial least squares

The content of insensitive agent is an important parameter that has been shown correlated with the combustion characteristic of double-base oblate spherical propellant (DOSP). This work focused on the feasibility of simultaneous monitoring the content of insensitive agent (dibutyl phthalate (DBP) and N, N'-dimethyl-N, N'-diphenylurea (C₂)) in DOSP by using near-infrared (NIR) spectroscope coupled with partial least squares (PLS). The optimal spectral intervals for creating models of DBP and C₂ corresponded to 5964 cm^-1-4212 cm^-1 and 6240 cm^-1-4380 cm^-1, respectively. It had been demonstrated that derivative tools were more suitable for spectral preprocessing as which had the lowest root mean squares error of cross-validation (RMSECV). The best-performance models of DBP and C₂ were built under 4 and 7 PLS factors, respectively. The results showed that the determination coefficients of calibration (R_c²) and the root mean squares error of calibration (RMSEC) were 0.9771 and 0.0173 for DBP; 0.984 and 0.0072 for C₂, respectively. Besides, the developed models exhibited excellent ability in prediction with the determination coefficients in prediction (R_P²) and the root mean squares error in prediction (RMSEP) of 0.9681 and 0.0275 for DBP, and of 0.9554 and 0.0107 for C₂, respectively. The residual predictive deviation (RPD) of prediction set were 5.68 and 5.12 for DBP and C₂, respectively. The average relative errors of the proposed and reference methods were 0.652% for DBP, and 0.429% for C₂, revealing a good correlation between the reference values and predicted values. Therefore, it concluded that the proposed plan has shown to be an attractive means since its efficient and highly accurate which could provide a better option for quality control in the large-scale production of DOSP.

Gunshot residue detection technologies—a review

Background

Gunshot residue (GSR) is a shred of important trace evidence which helps forensic scientists solve a huge range of incidents related to firearms. The identification of the shooter to bullet identification from a gunshot wound help reconstruct a scene of the crime.

Main body

The review of this scientific paper is based on gunshot residue, its composition, and the growing advanced technology which allow us to study about how GSR analysis help to identify and detect residues. Various methods are acquired to identify and analyze organic and inorganic residues present when ammunition is fired. The review highlights the composition of GSR, its collection methods, and analysis part which emphasize on all the methods developed so far. The use of conventional methods including colorimetric and instrumentation-based analysis and advanced technology including electrochemical technique for detecting residues from the last 50 years. Spot tests or chemical tests were performed but they degrade the sample and can sometimes cause hindrance with some other nearby material present at the crime scene. Instrumentation techniques including AAS, ICP-MS, SEM, SEM-EDX, GC, HPLC, etc. are discussed in detail. Mostly advanced electrochemical methods developed are for inorganic gunshot residues (IGSR), but some researchers worked on both residues. Also, the fabricated electrochemical cells are replaced by a single strip-based technique for easy detection. So, to combat these issues, various scientists are moving towards sensor-based methods for rapid and reliable detection. These methods are more user-friendly, sensitive, and cost-effective and provide rapid detection results.

Conclusions

This review results in the composition of GSR, its collection methods, and analysis using sophisticated methods that emphasize all the methods developed so far and it also culminates the merits and demerits of all detection methods.

Interpol review of gunshot residue 2016-2019

This review paper covers the forensic-relevant literature in gunshot residue analysis from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Armed with the Facts: A Method for the Analysis of Smokeless Powders by Ambient Mass Spectrometry

The work presented here follows several others in investigating what capabilities, if any, ambient mass spectrometry might have toward the analysis of compounds commonly associated with smokeless propellant powders. This family of instrumental techniques has attracted curiosity from the field of forensic science due to its desirable properties such as rapid collection of information-rich data, combined with minimal requirements for sample mass and preparation. Experiments were conducted with a "Direct Sample Analysis" ion source integrated with a time-of-flight mass spectrometer. The ionization behaviors of nitroglycerin, methyl and ethyl centralite, akardite, diphenylamine, nitrosodiphenylamine, and nitrated diphenylamine derivatives were investigated specifically, with accurate-mass data presented for each. Diphenylamine standards were used to demonstrate the performance of this instrument, which exhibited good response linearity across 1 order of magnitude and sub-nanogram detection limits. Thirty smokeless powder extracts, recovered from ammunition potentially in circulation within Australia, were analyzed to determine whether the technique is appropriate for rapid analysis of smokeless powder particles. Results demonstrated that the technique might be applied to compare individual particles with each other or to a database. Such a capability may be of value in the examination of explosive devices containing smokeless powder, postblast residues therefrom, or muzzle discharge from a close-range shooting. However, when efforts were made to detect residues from the hands of a volunteer shooter, only some returned positive results, and a high background signal from the sample collection stub indicates that detection using this instrument is thus far insufficiently reliable.