RESUMEN
Currently the great majority of the criminal acts have involved the use of firearms, for these reasons the evidences generate from these are one of the fundamental pillars of a forensic investigation. The firearm leaves evidence known as gunshot residue (GSR), which is principally composed of burnt and unburnt particles from the detonation, as well as fragments of the bullet, cartridge case, and the firearm. Gunshot residue (GSR) is produced when a firearm is discharged and large quantities of it can be transferred to an individual who has fired. SEM-EDX is the common technique used in the forensic laboratories, the analysis consists in detecting the particles and its elements. In this work we propose the use of X-ray Spectrometry by Total Reflection (TXRF) for the analysis of metals present in related samples in ballistic cases. The analysis was focused in the relationship of three elements present in GSR. A series of experiments with different persons firing gun of 9â¯mm was performed in a shooting range. Analytical XRFS signals corresponding to K line of Copper and L lines Barium and Lead were employed as the best discriminating variables. Machine Learning techniques, such as discriminant analysis, supported vector machines and partial least squares - discriminant analysis, enable the correct classification of all samples analyzed. A hundred samples were analyzed so far, this method has demonstrated a very high classification performance for detecting gunpowder residues in the skin.
RESUMEN
A study was undertaken to quantify the concentration of toxic and potentially toxic elements in samples of rice, rice crackers, rice noodles, infant cereals and rice vinegar available in the Argentine market. The determination of nine elements, namely, As, Cd, Cr, Hg, Ni, Pb, Sb, Se, and Zn in 29 samples was performed by inductively coupled plasma-mass spectrometry. Element concentrations spanned the range (ng g-1): As, 67-858; Cd, <0.2-24.0; Cr, 36.6-937; Hg, <50; Ni, 38.6-1040; Pb, <2.0-139; Sb, <3.0-24.7; Se, <8.4-178 and Zn, 129-32400. Mercury was not detected in any of the analyzed samples. The highest concentration (32.4⯵gâ¯g-1) was found for Zn in infant cereals that according to the label were added by the manufacturer. To assess accuracy, NIST 1568a rice flour was analyzed and results were in good agreement with certified values.