Ammunition encoding by means of co-doped luminescent markers

摘要

In forensics, the identification of gunshot residues (GSR) is a crucial point in firearm crime investigations. However, there is a lack of analytical methodologies to characterize the residues produced by non-toxic ammunition (NTA). To overcome this drawback, researchers have proposed the introduction of luminescent and chemical markers into ammunition. Luminescent markers, besides overcoming problems of NTA analysis, aid to identify and collect GSR by direct visualization of luminescent residues under UV radiation. Furthermore, the development of new markers with unique compositions has opened new perspectives about encoding ammunition. In this work, we propose the use of eight co-doped lanthanide metal-organic frameworks (Ln-MOF) [Y(1-x)Ln(x)(BTC)] (wherein BTC = trimesic acid) containing discrete concentration levels of Eu3+, Tb3+, Sm3+ and/or Yb3+ ions, as chemical barcodes for ammunition. To assess the method efficiency, we performed blind tests in which neither the shooters and the analyst had knowledge about the marker present in each cartridge that was fired. After shots, the residues were collected and analyzed by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) and video spectral comparator (VSC) to identify the marker used. As result, all of the markers were correctly identified. In addition, correlation between the residues collected at different locations (as hands, firearm and shooting area) was possible. Therefore, the encoding method proposed proved to be a powerful analytical tool for firearm crime investigations, providing a level of information that cannot be achieved with the current methodologies.