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

## TL;DR

This study explores using gel permeation chromatography and likelihood ratios to compare smokeless powders for forensic analysis in China.

## Contribution

The paper introduces a novel forensic method for comparing smokeless powders based on polymer properties rather than trace compounds.

## Key findings

- Gel permeation chromatography measured molecular weights and PDI values of 79 smokeless powder samples.
- Likelihood ratio evaluation helped interpret data for forensic comparisons between powders.
- The method shows potential for linking powders without relying on trace compound analysis.

## Abstract

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.