Analysis of organic gunshot residue permeation through a model skin membrane using ion mobility spectrometry

摘要

Identification and detection of gunshot residue (GSR) is useful in firearm related events and provides important evidence in trials and related cases. At present, methodologies based on the analysis of inorganic particles found in GSR are not amenable to rapid presumptive testing in the field or laboratory settings. An alternative is to target the organic analytes that are vaporized during the firing event and then re-condense on skin and other surfaces, such as clothing. Previous studies have demonstrated that the persistence of organic compounds, such as diphenylamine (DPA), from hand swabs of shooters as detected using commercial ion mobility spectrometry (IMS) instruments was 3–4 h. These same studies indicated that secondary transfer did not occur, which implied that losses of the organic compounds were attributable to absorption into the skin. The goal of this study was to assess the dermal absorption characteristics of organic gunshot residue (OGSR) using IMS. Two studies were conducted. First, a qualitative IMS method was developed for the in vitro analysis of select OGSR compounds. In vitro studies with medical grade silicone were conducted using Franz diffusion cells (FDCs). The results from this study demonstrated that OGSR was dermally absorbed. Second, a semi-quantitative IMS method was developed for an in vitro study of DPA. The skin permeability of DPA (Kp) was experimentally determined to be 2.6 × 10−2 cm/hr, the steady state flux (Jss) was 13 μg cm−2 hr−1, and the lag time was 8.9 h. The results show excellent correlation with the 3–4 h persistence previously reported.