Gunshot residues (GSR) provide important clues in forensic investigations. When cartridge containing conventional ammunition is fired, it is possible to detect several chemical substances, such as organic (naphthalene, 2,6-dinitrotoluene, 2,4-dinitrotoluene, diphenylamine, etc) and inorganic compounds (nitrite, sulphate, lead, barium, antimony, etc). The adoption of non-toxic ammunition (NTA) introduces significant challenges in the identification of GSR using conventional methods, as inorganic metal such as lead are not present.
This study proposes the integration of the luminescent and electroactive marker, rhodamine B, into ammunition to address these challenges. Rhodamine B, widely used as a dye in industry for coloring plastics, wool, silk, and paper, provides distinctive properties that facilitate the unique identification of ammunition. The primary aim of this research was to evaluate the forensic effectiveness of this fluorescent and electroactive marker. The ammunition selected for this investigation was 0.380 NTA from Auto Treina E00G 95 9r, provided by Companhia Brasileira de Cartuchos-CBC®. The shots were performed using a 0.380 caliber Taurus pistol. To assess the luminescent marker's performance in detecting GSR, a mixture of the marker and titanium dioxide was integrated into the gunpowder (10 wt%). After firing, the marked ammunition produced visible luminescent residues on the shooters' hands, firearms, and at the target. Under UV-C radiation (λ= 365 nm), orange luminescence appeared, greatly improving the ability to detect and identify the GSR. The results also demonstrated the thermal stability of rhodamine B under these conditions.
Sample collection involved the application of a layer of commercial skin gel over the hand of the shooter. After removing the dried gel, the sample was analysed by cyclic voltammetry (CV), utilizing a µStat 8000 Multi Potentiostat/Galvanostat, a Metrohm® Pt-SPE as the working electrode, with reference Ag and auxiliary Pt electrodes, in a 0.1 molL-1 Britton-Robinson Buffer Solution (pH 5.33) at 100 mV/s over a potential range from -0.4 V to +1.0 V. The GSR on the weapon and target was promptly detected using a conventional UV lamp, and could be analyzed directly from a swab soaked in electrolyte support. Nonetheless, collection of GSR from shooters ’ hands using skin gel is necessary as it prevents the possibility of injuries from UV radiation. Additionally, the use of gel allows the production of a transparent glove containing the shooter 's fingerprints.
The oxidation profile of rhodamine on the Pt-SPE poduced a well defined anodic peak current at +0.85 V (vs. Ag/AgCl), which was proportional to concentration. This innovative approach markedly enhances forensic GSR identification capabilities from non-toxic ammunition, paving new pathways for visualizing residue and improving sample collection from different types of ammunition and weapons.