Spectrophotometric Analysis of Nitrite in Gunshot Recentness Examinations from Non Toxic Ammunitions: Expanding the Frontiers of Forensic Chemistry

Abstract

Nitrite ions consist on an important chemical clue related to gunshot examination, concerning to estimation of the time since discharge. Current forensic laboratory methods for nitrite analysis in gunshot residues are well established for investigating conventional ammunition residues. However, the use of these methods to analyze the so-called ecological or “non-toxic” ammunition has been less studied. Here, we have developed a spectrophotometric flow injection analysis method to test nitrite in samples of “non-toxic” ammunition residues. The ammunition used in these experiments was the NTA (non-toxic ammunition) model, .38 caliber, We also investigated the kinetics of nitrite decomposition for this type of ammunition over time. Sulfanilic acid and 1-naphthylethylenediamine in acetic acid were used as colorimetric reagents. The linear dependence of the spectrophotometric signal on the nitrite concentration was as follows: A = 2.07 x 104 µmol-1 L [NO2-] + 6.78 x 10-3 with a correlation coefficient (r) of 0.9994. The standard deviation (SD) of the analytical curve was 3.17 x 10-3 resulting in a limit of detection (LOD) = 0.46 µmol L-1 and a limit of quantification (LOQ) = 1.56 µmol L-1. The proposed instrumental method was more sensitive than conventional colorimetric tests and permitted the detection window to be extended to 32 days while ensuring the safety and reliability required for forensic analysis, in comparison to 7-10 days usually proposed for conventional ammunition. Therefore, the proposed method can be safely employed in forensic laboratories for routine analysis of nitrite ions in GSR samples from ecological or “non-toxic” ammunition.