The GSR plays a major role in forensic science. In the analysis related to firearms, especially their range, and the severity of wounds. The GSR method helps to find out the cause at the crime scene or in the victim’s body is taken up using the GSR method.
What is a GSR?
The primer is caused to explode when a gun is used, it occurs when it is crushed by the force of the firing pin. This process releases- hot gases and particles inside the propellant igniting the chemicals and resulting in the firing. It determines the presence of these materials on the skin and clothing of subjects and surfaces such as vehicles.
Components of Gunshot Residues
- Primer formation
- Formation of propellant Barrel Scrapping
- Barrel Scrapping
- Projectile’s composition
Methods of Analysis of GSR
- Chemical Test
- Instrumental Analysis of GSR
- Griess reagent test: The analysis can be based on the formation of a diazonium salt when nitrite in acid solution gets reacted with a primary aromatic amine. This is to determine the nitrate presence in GSR. A dark red color spot indicates the presence of GSR.
- Modified Griess test: This process is the same as a Griess reagent test, but this includes a step for filtration using a paper sprayed with 2naphthyl amine sulphonic and citric acid. This test shows the presence of nitrate in GSR.
- Sodium Rhodizonate Test: In this test lead residue is commonly used these residues were taken from exhibits. This method shows the lead detection in GSR. The color of the result varies from blue to violet depending on the PH levels of the sample.
- Thin Layer Chromatography: In this test thin layer of silica gel is prepared or aluminum oxide is prepared this serves as a stationary phase then the analysis of the sample takes place. In simple words, Rf = Distance traveled by the components/Distance traveled by the moving liquid phase.
Instrumental Analysis of GSR
SEM: The Scanning electron microscope with an energy dispersive X-ray analyzer. This equipment is usually used to detect electrons generated by the different processes to get images, secondary and backscattered, and for compositional analysis, the X-rays were used.
Process: In SEM a fine beam of the electron is focused on the material placed. When that beam collides with the specimen placed, the reaction takes place by way of some electrons reflects which is called backscatter. This gives a three-dimensional image. This process emits X-rays those rays are used to find the elemental composition of particles.
- GFAAS: The Graphite Furnace Atomic Absorption spectroscopy is a quantitative analysis method for tracing elements of primer residue Viz., lead, Barium, antimony, etc. An electron absorbs the radiation of the same wavelength while the same gets excited.
- ICP-MS: The inductively coupled Plasma-Mass Spectroscopy is a method used to measure traces of primer residue such as lead, Barium, and antimony. This works by coupling an argon plasma to a radio frequency electromagnetic field at atmospheric pressure.
- CE: The capillary Electrophoresis is used to find the organic components in gunshot residue. This method separates and detects organic and explosive material components as it is also a bulk method analysis.
Collection of Gunshot Residues
Wet method: The inorganic contents of GSR are commonly collected using 5% nitric acid.
Tape Lifting: This method is commonly used in taking fingerprints and explosive or gunshot residue analysis.
Swabbing: The collection of samples using an adsorbent surface is called swabbing. This method is used in both organic and inorganic sample collection.
Glue Lift method: The Glue lift method is used more than the Tape lift method. This is due to the sample collected from glue containing less number of interfering particles when SEM was performed as reported by Basu et al. (Basu et al., 1997)
Vacuum Lift method: Zeichner et al., 2003 in their paper developed a filter for collecting organic gunshot residue samples viz., fiberglass, and Teflon. It is also used in collecting samples from clothing as it is more suitable than the tape method which lifts of debris or other fiber material.
Collecting using Human Mucus: Human noses do the process of filtration of air, while this happens it arrests fine particles in between nose hairs. When a firearm is blown it releases some gases which got arrested in these hairs.
Collected from Hair: When it comes to curly hair it will have very fine teeth and hence it encounters more residues comparatively. The hairs of the person who stood near a gunshot show unburned powders.
The Gunshot Residue analysis gets its importance because of the increasing crimes with guns. The above-written article is an outline of the Method of analysis of GSR. This will change according to the new invention and in the evolution of new techniques.