Describe the scientific methods employed to detect firearm residues.

Question

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Answer 1

Detecting firearm residues on the hands of an individual may be of great importance in evaluating deaths caused by gunshot wounds. Detection of such residues on the hands of a deceased individual is often confirmatory evidence of a suspected suicide.
One of the earliest methods of determining whether an individual discharged a weapon, the paraffin test or dermal nitrate test, was based on the detection of nitrates on the surfaces of the hands. Paraffin was employed for the removal of powder residues from the hands. Diphenylamine was the reagent used to detect the nitrates picked up by the paraffin. This test is no longer considered valid, because no distinction can be made between nitrates of gunpowder origin and those from other sources, which are quite commonly encountered in day-to-day living.
A series of chemical spot tests for detection of metallic components of firearm discharge residues was developed. Such metallic substances originate mainly from the primer, although they can also come from the bullet or cartridge case. Spot tests were developed for the presence of antimony, barium, and lead substances found in most primers. These tests are inconclusive because they are essentially qualitative rather than quantitative.
Compounds of antimony, barium, and lead are used in modern noncorrosive primers. When a handgun is discharged, discrete particulate matter containing these elements are deposited on the thumb, forefinger, and connecting web (the back of the hand holding the weapon). The metallic compounds are removed from the hand, either with paraffin or, more commonly, with cotton swabs saturated with a dilute solution of acid. This material is then submitted for analysis.