Method validation for the determination of propellant components by Soxhlet extraction and gas chromatography/mass spectrometry

Chemical Analysis of Gunpowder and Gunshot Residues

The identification of firearms is of paramount importance for investigating crimes involving firearms, as it establishes the link between a particular firearm and firearm-related elements found at a crime scene, such as projectiles and cartridge cases. This identification relies on the visual comparison of such elements against reference samples from suspect firearms or those existing in databases. Whenever this approach is not possible, the chemical analysis of the gunpowder and gunshot residue can provide additional information that may assist in establishing a link between samples retrieved at a crime scene and those from a suspect or in the identification of the corresponding model and manufacturer of the ammunition used. The most commonly used method for the chemical analysis of gunshot residue is scanning electron microscopy with energy dispersive X-ray, which focuses on the inorganic elements present in ammunition formulation, particularly heavy metals. However, a change in the legal paradigm is pushing changes in these formulations to remove heavy metals due to their potential for environmental contamination and the health hazards they represent. For this reason, the importance of the analysis of organic compounds is leading to the adoption of a different set of analytical methodologies, mostly based on spectroscopy and chromatography. This manuscript reviews the constitution of primer and gunpowder formulations and the analytical methods currently used for detecting, characterising, and identifying their compounds. In addition, this contribution also explores how the information provided by these methodologies can be used in ammunition identification and how it is driving the development of novel applications within forensic ballistics.

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.

A simple and safe approach for simultaneous spectrophotometric determination of nitroglycerin and nitrocellulose in double base solid propellants

An accurate, simple and safe method was developed for simultaneous determination of nitroglycerine (NG) and nitrocellulose (NC) in double base solid propellants (DB propellants). The proposed method is based on alkaline hydrolysis of NG and NC, and followed by colored reaction of released nitrite ion with p-nitroaniline in the presence of diphenylamine in acidic media and produce azo dye. The absorbance of the azo dye was measured at 534 nm. Two sets of reaction conditions were developed. In the first set, at room temperature, only NG was hydrolyzed and calibration curve obtained. In the second set, at 60 ℃, NG and NC were hydrolyzed simultaneously. Based on obtained amount for the NG at room temperature, and total amount of NG and NC at 60 ℃, the amount of NC was determined by using stoichiometric equations. The calibration curve was linear over the concentration ranges of 0.2-5.0, 0.5-10 μg mL^-1 for NG and NC, respectively. The proposed method was successfully applied for the determination of NG and NC in DB propellants with good recoveries ranged from 99 to 101%, and RSD less than 2.0%. The method statistically compared based on t- and F-tests with those obtained in according to military standard method (MIL-STD-286). The results showed that the proposed method offers an accuracy and reliable approach for the determination of these compounds in DB propellants, and can be suggested as a routine method in military quality control laboratories.

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.

Improved Quality of Corn Silage When Combining Cellulose-Decomposing Bacteria and Lactobacillus buchneri during Silage Fermentation

This study aimed to investigate the effects of the combined use of cellulose-decomposing bacteria (CDB) and heterolactic lactic acid bacteria (LAB) on corn silage fermentation. Fresh maize was treated with heterolactic LAB or CDB combined with heterolactic LAB inoculants or without any treatment. Chemical and microbiological analyses were conducted at specific times after ensiling. A comprehensive value evaluation was conducted using the principal component analysis model. Although all treatments significantly affected the microorganism numbers during fermentation, the numbers of aerobic bacteria, LAB, yeast, and molds in the groups with combined CDB and LAB were significantly higher than those in the group with LAB only (P < 0.05). All treatments regulated the silage CO₂ production. Each treatment had different effects on the nutrient degradation rate. Based on a comprehensive evaluation, the CDB and heterolactic LAB combination had the best effect on the ensiling process in improving the quality and feed value of corn silage.

Reversed-phase vortex-assisted liquid-liquid microextraction: a new sample preparation method for the determination of amygdalin in oil and kernel samples

A novel, simple, and rapid reversed-phase vortex-assisted liquid-liquid microextraction coupled with high-performance liquid chromatography has been introduced for the extraction, clean-up, and preconcentration of amygdalin in oil and kernel samples. In this technique, deionized water was used as the extracting solvent. Unlike the reversed-phase dispersive liquid-liquid microextraction, dispersive solvent was eliminated in the proposed method. Various parameters that affected the extraction efficiency, such as extracting solvent volume and its pH, vortex, and centrifuging times were evaluated and optimized. The calibration curve shows good linearity (r(2) = 0.9955) and precision (RSD < 5.2%) in the range of 0.07-20 μg/mL. The limit of detection and limit of quantitation were 0.02 and 0.07 μg/mL, respectively. The recoveries were in the range of 96.0-102.0% with relative standard deviation values ranging from 4.0 to 5.1%. Unlike the conventional extraction methods for plant extracts, no evaporative and re-solubilizing operations were needed in the proposed technique.

A fully validated method for the determination of arsenic species in rice and infant cereal products

A full validation of inorganic arsenic (iAs), methylarsonic acid (MA), and dimethyl arsinic acid (DMA) in several types of rice and rice-based infant cereals is reported. The analytical method was developed and validated in two laboratories. The extraction of the As species was performed using nitric acid 0.2 % and hydrogen peroxide 1 %, and the coupled system liquid chromatography-inductively coupled plasma-mass spectrometry (LCICP-MS) was used for speciation measurements. Detection limit (DL), quantification limit, linearity, precision, trueness, accuracy, selectivity, as well as expanded uncertainty for iAs, MA, and DMA were established. The certified reference materials (CRMs) (NMIJ 7503a, NCS ZC73008, NIST SRM 1568a) were used to check the accuracy. The method was shown to be satisfactory in two proficiency tests (PTs). The broad applicability of the method is shown from the results of analysis of 29 samples including several types of rice, rice products, and infant cereal products. Total As ranged from 40.1 to 323.7 μg As kg–1. From the speciation results, iAs was predominant, and DMA was detected in some samples while MA was not detected in any sample.