Quantification of smokeless powder (SLP) additives on hands after direct handling of bulk samples via a filter-and-shoot method

Abstract

Smokeless powders (SLPs) are easily available energetic materials that are often used in the construction of improvised explosive devices. Following a bombing incident, hand swabs are routinely collected from persons of interest (POIs) to assess potential SLP handling. However, the evidential significance of analytical findings remains difficult to assign due to the lack of systematic data on residue transfer. This study aimed to address this gap by determining the quantities transferred to hands (qT) of three common SLP additives – diphenylamine (DPA), dibutyl phthalate (DBP), and ethyl centralite (EC) – following direct handling of bulk samples, with the specific goal of enabling the estimation of expected qT ranges on a POI's hands under the hypothesis that they had handled SLP. A streamlined filter-and-shoot method was developed for residue collection and analysis, allowing direct chromatographic analysis without preconcentration steps. The results showed that qT values typically ranged from the high nanogram to low microgram level, with DBP exhibiting the highest values and EC the lowest, mirroring their relative concentrations in the SLP formulations. The total mass of SLP handled (MSLP) and the handler variability (HID) were identified as significant factors influencing qT, whereas the type of SLP (TSLP) had a much weaker effect. Notably, a strong linear dependence between qT and MSLP was observed for all the three compounds. Based on these findings, regression models were developed to estimate expected qT ranges (including means and standard deviations) at different MSLP values, providing a practical tool to refine interpretation where information on the amount of SLP handled is available. By establishing empirical data on SLP residue transfer, this study fills a critical knowledge gap in the literature, enhancing the ability to assess the significance of forensic findings and ultimately contributing to more robust interpretations in cases involving suspected SLP handling.