Forensic comparison analysis of smokeless powders by gel permeation chromatography and likelihood ratio evaluation methods

In China, the use of smokeless powders for making homemade ammunition and bombs is an incipient criminal practice. One of the key tasks of analyzing smokeless powders in forensic sciences is to make comparisons between them, providing information about their source or establishing a link between two different smokeless powders seized at different locations. The main component of smokeless powders is nitrocellulose (NC) no matter what type of the smokeless powder is. As a kind of polymer, NC may have different molecular weights and polydispersity index (PDI) values, which could help the identification and differentiation of the smokeless powders. In this study, weight-average molecular weights (Mw), number-average molecular weights (Mn), and PDI value of 79 propellants samples from different sources were measured by gel permeation chromatography, and likelihood ratio evaluation method was applied to facilitate interpretation of the data. The possibility of using these methods to make comparisons between smokeless powders was explored instead of depending on analysis of target compounds with trace amounts in them.