Raman Spectroscopic Analysis of Gunshot Residue Offering Great Potential for Caliber Differentiation

Abstract

Near-infrared (NIR) Raman microspectroscopy combined with advanced statistics was used to differentiate gunshot residue (GSR) particles originating from different caliber ammunition. The firearm discharge process is analogous to a complex chemical reaction. The reagents of this process are represented by the chemical composition of the ammunition, firearm, and cartridge case. The specific firearm parameters determine the conditions of the reaction and thus the subsequent product, GSR. We found that Raman spectra collected from these products are characteristic for different caliber ammunition. GSR particles from 9 mm and 0.38 caliber ammunition, collected under identical discharge conditions, were used to demonstrate the capability of confocal Raman microspectroscopy for the discrimination and identification of GSR particles. The caliber differentiation algorithm is based on support vector machines (SVM) and partial least squares (PLS) discriminant analyses, validated by a leave-one-out cross-validation method. This study demonstrates for the first time that NIR Raman microspectroscopy has the potential for the reagentless differentiation of GSR based upon forensically relevant parameters, such as caliber size. When fully developed, this method should have a significant impact on the efficiency of crime scene investigations.

Recent trends in organic gunshot residue analysis

“…The application of Raman spectroscopy to the analysis of OGSR compounds was first reported in 2012 [54,74]. It was successfully used for the detection of MC, EC, dinitrotoluene, DPA and its nitration products [54,74].…”

“…It was successfully used for the detection of MC, EC, dinitrotoluene, DPA and its nitration products [54,74]. The authors reported that the OGSR spectrum showed high similarity with the spectrum of the unfired ammunition, which enabled the OGSR to be traced back to the ammunition used.…”

“…This study was performed from the point of view that the specific firearm parameters are responsible for the combustion process and that the chemical composition of specific ammunition is dependent upon the calibre and that as such this calibre-firearm pair would determine the subsequent GSR product. The authors reported the potential for a rapid, portable, solventless and selective alternative for GSR identification, while providing a statistical and chemical link between the suspect and the crime scene [74]. In order to further improve the statistical discrimination of GSR, complementary spectroscopic data from Raman and Fourier Transform Infrared FTIR spectroscopy were combined into a single dataset, in a later study by Bueno and Lednev [75].…”

Tiro-aztarnen identifikazioa, auzitegi-laborategien erronka

“…Azkeneko urteotan, teknika horrek konposatu organikoen identifikazioa ahalbidetu du [39]. Metodologia estatistikoekin batera, espektroskopia hau munizioaren kalibrea ezagutzeko ere erabili da [40]. Ta pektroskopia konbinatzen dituen metodo analitikoa garatu dute eta munizio berdeek sortutako partikulak analizatu dituzte [32].…”

Copper Determination in Gunshot Residue by Cyclic Voltammetric and Inductive Coupled Plasma-Optical Emission Spectroscopy

“…Analysis of organic compounds in GSR was implemented by a combination of solid-phase microextraction (SPME) and gas chromatography mass spectrometry (GC-MS) technique [10], desorption electrospray ionization mass spectrometry (DESI-MS) [5] and fourier transform infrared (FTIR) spectroscopy [11].…”