The Research On Analysis Method Of Stable Isotope Ratio Characteristic Of Black Powder

Due to its uncomplicated production process and ready availability of raw materials,black powder is one of the most common explosives in explosive cases.It is essential for sustaining national security and combating crime to analyze and trace black powder in criminal cases.In China,the current examination procedure for black powder is limited to component analysis and cannot be compared or traced back to its source.The stable isotope ratio of black powder changes according to the origin of the raw materials and the production process.Therefore,stable isotope ratio can be an indispensable indicator for comparative analysis and tracing of black powder.The stable isotope ratio mass spectrometry（IRMS）has been widely used in the field of food safety and environmental protection.Although there have been few reports on the use of IRMS in comparing and tracing black powder abroad,there has not been thorough research on this topic.In addition,no research has been conducted on stable isotopes of black powder in China,and the characteristics,traceability,and influencing factors of stable isotopes of black powder in China are poorly understood.This paper seeks to investigate and establish a method for analyzing the stable isotope ratio characteristics of black powder in order to provide technical support for tracing its source.The specific contents of the research are as follows:（1）A method for analyzing stable isotope ratios of black powder has been investigated and developed.The sample amount,dilution ratio,combustion temperature,column temperature,and standards were optimized and selected.The sample amount for carbon（C）and nitrogen（N）stable isotope analysis has been determined to be 350±20μg,the dilution ratio was 70%for C stable isotope detection,the column temperature was 65℃,the combustion temperature was900℃,the C standard was IAEA-CH-7/IAEA-602/USGS62,and the N standard was USGS34/USGS62/USGS32.The sample amount for oxygen（O）stable isotope analysis has been determined to be 200±20μg,the combustion temperature was 1350℃,the temperature of the chromatographic column was 80℃,and the standard material was USGS34/USGS35/USGS2.Before sample analysis,a pre-processing method for black powder samples involving pulverizing and desulfurization was also established.The accuracy and precision of the proposed method for the pretreatment of black powder samples and the determination of stable isotope ratios of carbon,nitrogen,and oxygen were superior to those reported in the literature.（2）The determination of the stable isotope ratio characteristics of black powders from various sources.Stable isotope ratio analysis were performed on 25 samples from 19 manufacturers in China’s main black powder production regions.The results revealed substantial differences inδ¹³C、δ¹⁵N andδ¹⁸O between black powders from different manufacturers and between production batches separated by lengthy time intervals.In forensic science research,stable isotopes can differentiate between black powders with consistent components by comparing them to black powders from various manufacturers.（3）The Investigation of the relationship between the stable isotope ratios of black powder and raw materials.Utilizing various potassium nitrate and carbon powders,six distinct varieties of black powder were manufactured.Separate analysis with stable isotopes were conducted on unprocessed materials and black powders.Analysis of various manufacturers’raw materials revealed that the majority of carbon samples originated from C₃ plants,whileδ¹³C values for different types of carbon exhibited significant differences;potassium nitrate from different manufacturers or batches also exhibited significant differences.Overall,the results of the analysis indicate that the stable isotope ratio of black powder is identical to its raw material ratio,and the two are highly correlated.（4）The determination of variations in stable isotope ratios before and after black powder ignition.Six distinct varieties of homemade black powder were ignited to investigate changes in stable isotope ratios prior to and after ignition.Before and after ignition,there were significant differences inδ¹⁵N andδ¹⁸O;when carbon was not completely burned during the experiment,there was no significant difference inδ¹³C;when the reaction was complete,there was a significant difference inδ¹³C;and there was a significant positive correlation betweenδ¹³C、δ¹⁵N andδ¹⁸O of black powder and combustion residues.At the same time,the impacts of various extraction methods on the analysis were investigated.Cotton swab wiping and water-soluble extraction methods were found to substantially alter the stable isotope ratio values of black powder combustion residues compared to solid residue analysis collected directly.In actual circumstances,it is recommended that solid residue from black powder explosions be collected directly for stable isotope analysis.（5）The determination of the impact of sulfur on the stable isotopes of black powder.To determine the sulfur content of black powder,a gas chromatography-mass spectrometry method was developed,and the sulfur content of black powder from various manufacturers was measured.The results revealed that the sulfur content of different manufacturers’black granules varied significantly from 98.84 g/mg to 271.55 g/mg.During the stable isotope analysis procedure,sulfur would precipitate,negatively impacting the reproducibility and stability of the analysis results and causing particular damage to stable isotope ratio mass spectrometers.This study established a desulfurization method that can efficiently remove sulfur from black powder without causing significant fractionation of stable isotopes,thereby enhancing the stability of δ¹³C、δ¹⁵N andδ¹⁸O value analyses for black powder.In this paper,the established method was applied to the analysis of black powder samples from actual cases,resulting in the successful separation of 12 black powder samples based on three stable isotope dimensions:δ¹³C、δ¹⁵N andδ¹⁸O.The results demonstrated that the established technique for stable isotope analysis of black powder could be used for precise differentiation of actual black powder samples and provided technical support for comparison and source tracing of black powder involved in similar cases.