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US scientists reported to the American Chemical Society annual meeting in April how they have developed a highly dependable, fast and inexpensive method for identifying gunshot residues at crime scenes. Analysis of gas chromatography data coupled with results from a nitrogen phosphorus detector are used to identify trace quantities. Because of environmental and health concerns surrounding the use of lead, "lead-free" ammunition has become commonplace. However, conventional forensics tests relied on the presence of lead in gun-shot residues to provide crime scene evidence. Now, Jorn Chi Chung Yu, Garrett Lee Burleson, and colleagues in the Department of Forensic Science at Sam Houston State University in Texas have devised a new sampling and analysis approach that circumvents the problem of a lack of lead. The technique requires just a tiny speck of residue and uses no extraction reagents, but could boost the accuracy of forensics significantly, Burleson explains. "Gunshot residue tests are done in almost every case where a shooting has taken place," Burleson says, "The main focus of our research is to develop a method that will help credibility of gunshot residue evidence in court. You can get results in 30 to 40 minutes with the new test. In addition you only need small amounts of evidence to run the test." Burleson points out that of the current forensics methods for analysing gunhot residues, most are susceptible to outside interferences that can lead to false positives or false negatives. Moreover, it is the presence of lead that is essential to a valid reading for many of the standard tests, such as the sodium rhodizonate test and scanning electron microscopy with energy dispersive X-ray detection. Modern environment friendly ammunition [there's irony, Ed.] are now using aluminium and zinc alloys instead of lead, which presents a problem to forensic scientists. "When a gun fires, the gunpowder explodes, producing gases at enormous pressure that propels the bullet out of the barrel of the firearm," Burleson adds. "Some of the residue from that explosion is deposited on the hands of the shooter and the clothing of the victim." Burleson and his colleagues have used solid phase micro-extraction combined with gas chromatography to home in on the chemicals present in that ejected material. "When you have a residue particle, no matter how small, it's going to contain signatures of every element in that powder," Burleson adds, and these signatures offer a wider range of detection possibilities compared to traditional methods. "If you're looking for powder rather than a fragment of lead, there's a lot more of it," he adds, "You're getting more of the residue to analyze. It makes it a much more efficient method of detection." For example, a distinctive combination of certain chemicals, such as diphenylamine, ethyl centralite and nitrodiphenylamine, is typically found only in explosive mixtures and therefore allows for a simple analysis of gunplay at a crime scene. Burleson's test could be used as a preliminary or confirmatory one. "As far as a stand-alone test, it's an excellent, reliable and cheap test to do," he said. "But for the sake of clarity and thoroughness, examiners will usually run multiple tests, such as the sodium rhodizonate test at the crime scene, and they could then confirm the findings with my method." "Single gun powder particle analysis was demonstrated for the first time under an optimized SPME-GC-NPD condition. We believe the method offered an incredible potential to identify explosives, plasticizers, and trace amount of additives from gunshot residue evidence for forensic applications," Burleson says. He concedes that this method will not replace current preliminary tests such as the Modified Griese Test and the Sodium Rhodizonate Test, but rather confirm their results and perhaps provide a definitive answer in the event that a false positive or negative result occurs in the absence of a lead residue. The approach has additional benefits as well as speed and accuracy in that the novel extraction method requires no reagents of solvents and so is safer and more cost effective than other methods. Related links:
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