Estimating Diphenylamine in Gunshot Residues from a New Tool for Identifying both Inorganic and Organic Residues in the Same Sample

Ana Argente-García,Lusine Hakobyan,Pilar Campíns-Falcó,Carmen Guillem

doi:10.3390/separations6010016

Abstract

A method involving the collection and determination of organic and inorganic gunshot residues on hands using on-line in-tube solid-phase microextraction (IT-SPME) coupled to miniaturized capillary liquid chromatography with diode array detection (CapLC-DAD) and scanning electron microscopy coupled to energy dispersion X-ray (SEM-EDX), respectively, for quantifying both residues was developed. The best extraction efficiency for diphenylamine (DPA) as the main target among organic residues was achieved by using a dry cotton swab followed by vortex-assisted extraction with water, which permits preservation of inorganic residues. Factors such as the nature and length of the IT-SPME extractive phase and volume of the sample processed were investigated and optimized to achieve high sensitivity: 90 cm of TRB-35 (35% diphenyl, 65% polydimethylsiloxane) capillary column and 1.8 mL of the processed sample were selected for the IT-SPME. Satisfactory limit of detection of the method for analysis of DPA deposited on shooters’ hands (0.3 ng) and precision (intra-day relative standard deviation, 9%) were obtained. The utility of the described approach was tested by analyzing several samples of shooters’ hands. Diphenylamine was found in 81% of the samples analyzed. Inorganic gunshot residues analyzed by SEM-EDX were also studied in cotton swab and lift tape kit samplers. Optical microscopy was used to see the inorganic gunshot residues in the cotton swab samplers. The lift tape kits provided lesser sensitivity for DPA than dry cotton swabs—around fourteen times. The possibility of environmental and occupational sources could be eliminated when DPA was found together with inorganic residues. Then, the presence of inorganic and organic residues in a given sample could be used as evidence in judicial proceedings in the forensic field.

Highlights

Chemical and physical evidence such as gunshot residues (GSRs) from firearms discharge may provide valuable forensic information [1,2]
Inorganic gunshot residues (IGSRs) are usually spherical particles mainly composed of Ba, Pb, Separations 2019, 6, 16; doi:10.3390/separations6010016
False positive results can be produced from inorganic particles derived from environmental and occupational sources [10,11,12,13], which is a problem when considering IGSRs as evidence in judicial proceedings in the forensic field

Summary

Introduction

Chemical and physical evidence such as gunshot residues (GSRs) from firearms discharge may provide valuable forensic information [1,2]. Gunshot residues are organic and inorganic components in nature, which can be deposited on a shooter’s body, mainly onto the index fingers and thumbs of the hands, after discharging a firearm [3]. Other elements such as Ca, Al, Cu, Fe, Zn, Ni, Si, and K can be found [5], they are more prevalent in the environment than Pb, Ba, and Sb [6] The size of these particles is usually from 0.5 μm to 10 μm, sizes up to 100 μm have been reported [7]. The analysis of organic gunshot residues (OGSRs) in the same sample could provide complementary information that could strengthen the probative value of a forensic sample. Organic components originate mostly from the propellant, and their composition depends on the commercial brand and ammunition type

Objectives

Methods

Conclusion