Detection of organic gunshot residue in smokeless powders using an on-site analytical approach
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Citation
Abstract
Violence due to firearms has been an issue in the United States for numerous years. Due to the continuation of violence through the utilization of firearms, it is very important for law enforcement and forensic scientists to have various methods to detect and identify components of ammunition that have been discharged. These components, also known as gunshot residue, are usually left in trace amounts, meaning it cannot be seen to the unaided eye. These trace amounts are very important in identifying the shooter during an investigation, so it is crucial to have a sensitive and specific analytical method to detect the gunshot residue. There are two types of Gunshot Residue: Inorganic Gunshot Residue (IGSR) and Organic Gunshot Residue (OGSR). Most firearm evidence that is examined focuses on IGSR and uses analytical techniques such as Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS) to detect it. Transferability of IGSR is not uncommon when detecting IGSR on a suspect, so it is very important to create an analytical approach that is rapid and reliable for detecting Organic Gunshot Residue. The persistence and collection of OGSR has many benefits in comparison to IGSR, so finding a way to both collect and analyze OGSR would be valuable to both law enforcement and laboratory analysts. In recent years, new methods have been developed to detect the organic compounds discharged from firearms. One method that has been successful in the detection of OGSR compounds is the time-of-flight secondary ion mass spectrometer. The drawback to many methods of detecting GSR components is that it is very time consuming. One common and accepted technique for detecting OGSR has not been created. During this research, a field portable, High Pressure Mass Spectrometer called the MX908 was used to create a library using the organic compounds Dibutyl Phthalate (DBP), Diphenylamine (DPA), Ethyl Centralite (EC), Nitroglycerin (NG), and Nitroguanidine (NQ) in the Explosives Hunter (EH) and Chemical Warfare Hunter (CWH) mission modes. After a library was created and validated on the device, assorted brands of smokeless powders, both burnt and unburnt, were tested to determine the accuracy of the library by analysis of the powders. The MX908 demonstrated the ability to detect the OGSR components in the validation studies conducted and the smokeless powder testing. When conducting the validation studies, CWH mode, a predetermined, on-device method, was better at identifying the target compounds while producing the least number of false positives. NQ, EC, DBP, DPA, and NG were reliably detected in both CWH and EH mode. There were a significant number of false positives in EH mode for NQ and DBP. Contrary to the validation testing, when testing the smokeless powders, EH mode had greater accuracy and no false positives. EC, DBP, NG, and DPA were detected in EH mode for both unburnt and burnt samples. DPA, EC, and DBP were detected in CWH mode for the smokeless powder samples. The unburnt samples tested in both EH mode and CWH mode had more red alarms than the burnt residue samples. This was expected because as smokeless powder burns, some of the components are consumed.
Description
2024