Discharge residue detection firearms

Since both methods yield comparable results, which method should a laboratory use for firearms discharge residue detection Three factors must be kept in mind cost, turn-around-time and personnel requirements. 

Development of Firearm Discharge Residue Detection Techniques... 

J. S. Wallace, Firearms Discharge Residue Detection Using Flameless Atomic Absorption Spectrophotometry, AFTE Journal 19, no. 3 (July 1987). 

Development of a Method for Organic Firearm Discharge Residue Detection... 

Several techniques have been utilized for the detection of firearms discharge residue on the hands of an individual who has recently handled or discharged a weapon. Testing for the presence of nitrates proved unreliable and was discarded. Colorimetric tests for barium and antimony from primer composition were found to lack sufficient sensitivity for general application. 

Neutron activation analysis (NAA) with a rapid radiochemical separation has been the method generally used in recent years, but requires substantial investment, has high operating cost and limited availability. Modem flameless atomic absorption (AAS) instruments provide sensitivity approaching that of NAA and offer a viable alternative for the detection of firearms discharge residue. 

In 1959 Harrison and Gilroy (3) demonstrated the detectability of barium, antimony and lead in firearm discharge residue using a specific "spot" test for each element. Inadequate colorimetric sensitivity for barium and antimony (I4.) has severely restricted the use of the method as a field tool. 

The development of neutron activation analysis (NAA) as a sensitive and specific method of trace elemental analysis led to its application during the 1950 s for the detection of firearm discharge residue. Its ability to detect and identify very low concentrations of barium and antimony, elements associated with most primer compositions, was encouraging. 

Table III shows that two quite different analytical techniques, Flameless Atomic Absorption Spectroscopy and Neutron Activation Analysis, yield equivalent frequencies of detection of firearms discharge residue.

Firearm discharge residue consists of a complex heterogeneous mixture that is claimed to be mostly particulate in nature.105 Particulate matter can be detected on a suspect, but the possibility of vaporized/gaseous products being adsorbed on to skin or clothing surfaces also exists. 

S. S. Krishnan, K. A. Gillespie, and E. J. Anderson, Rapid Detection of Firearm Discharge Residues by Atomic Absorption and Neutron Activation Analysis, Journal of Forensic Sciences 16 (1971) 144. 

Apart from various gases four types of particles have been detected in firearm discharge residue ... 

At the start of 1978 the particle analysis method183 replaced the flameless atomic absorption bulk elemental method184 as the firearm residue detection method in the NIFSL. Since then the particle analysis method has been substantially improved by the use of a sample concentration/cleanup procedure,185 the addition of a backscattered electron detector, and the development of an automated residue detection system.186 187 Despite these improvements the technique remains costly and labor intensive. Certain aspects of the system required further work, in particular, the particle classification scheme discharge particles from mercury fulminate-primed ammunition and discharge particles from new primer types (Sintox). 

The work serves to illustrate the heterogeneous nature of firearm discharge residue particles and to clarify the types of particles detected. 

The remainder of the book details chemical aspects of forensic firearms casework with particular emphasis on the detection of gunshot residues (GSR)/firearm discharge residues (FDR)/cartridge discharge residues (CDR) on a suspect s skin and clothing surfaces. The development of an analytical method to routinely examine samples from terrorist suspects for both firearms and explosives residues is described. 

To overcome the problem of false positives it is now more usual, whenever possible, to use a scanning electron microscope to detect the metals, such as barium, associated with discharging of a firearm while the organic constituents of smokeless powder are preferably analyzed as for explosive residues above, i.e., by using LC followed by MS confirmation, GC-MS, etc. 

Overall, the possibility of determining the bullet jacket material from the residue around the bullet hole does not appear to be feasible using FAAS. However, FAAS reliably detects elements associated with firearm discharge on the perimeter of the bullet hole and is a very useful method for confirming bullet damage. 

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