Desulfurization of black powder for isotopic profiling using isotope ratio mass spectrometry

The stable isotope analysis of black powder is of utmost significance with regard to its further comparison and traceability in explosion-related cases. To date, only a limited number of studies have reported the stable isotope analysis of black powder using isotope ratio mass spectrometry (IRMS). However, because the sulfur content in black powder is high, sulfur deposition is extremely likely during the analysis process, thereby damaging the instrument and affecting the reproducibility of the results. Therefore, desulfurization of black powder samples prior to IRMS analysis is extremely desirable. Herein, based on the difference in the solubility of black powder components, chloroform was selected to desulfurize black powder. The results demonstrated that chloroform extraction could effectively eliminate sulfur from the black powder. The isotope fractionation effect caused by desulfurization was also studied. The changes in δ¹³C, δ¹⁵N, and δ¹⁸O after desulfurization were close to the standard deviation values and did not affect the analysis of black powder. Desulfurization and stable isotope analysis were performed on 12 black powder samples obtained from cases that happened in eight different areas in China, and the carbon, nitrogen, and oxygen isotope ratios in all the samples were effectively distinguished. Therefore, the established method can successfully distinguish the stable isotope ratios in black powder samples using IRMS after desulfurization while avoiding damage to the instrument and enhancing the stability of the results.