A Comparative Study of SEM-EDX and ICP-MS Detection Based on Gunshot Residue Originated from AK-47 and M16 Rifles

Abstract

This is a comparative study on Gunshot Residues (GSR) originated from AK-47 and M16 rifles by SEM-EDX and ICP-MS. The GSR samples were obtained from multiple body parts of the shooter (hand, cloth and helmet) with elapsed times, as well as from multiple shooting occasions. The SEM-EDX data established the different shapes and dimensions of the GSR samples and the presence of "unique particles". These particles had different elemental combinations with elements such as Pb, Ba and Sb. An automated search system was used for counting the number of 3-elements (Pb, Ba and Sb) called "characteristic particle". The samples collected from M16 showed higher number of characteristic particles than that of the AK-47. The existence of characteristic particles ranged from zero to big numbers and were different for different collecting positions. Right-lower arm gave the highest number of particles. The increase in number of shots led to an increase in single-element particles such as Pb and Sb. Number of particles was independent of the time between firearm shooting and sample collection. ICP-MS analysis showed that the heavy metal concentration increased with the number of shootings for the same source. Sb, Ba and Pb concentrations varied with the various parts of sources. The concentrations of GSR particles decreased when the elapsed time increased. These results concluded that SEM-EDX can establish the unique particles and their elemental composition and that the ICP-MS can quantify the precise concentration of heavy metals in the GSRs.