When it comes to establishing time of death from skeletal remains, diffuse reflectance near-infrared spectroscopy just makes sense to Kenneth W. Busch.
“It doesn’t require any sample prep, and it’s nondestructive,” said Busch, professor of chemistry at Baylor University’s Center for Analytical Spectroscopy in Waco, Texas. “That’s an interesting point when you’re talking about evidence, because they hate to have you dissolve it. ‘Sir, we dissolved your exhibit No. 1’ – that’s a problem.” Before Busch began his project, determining postmortem interval, or PMI – the elapsed time since death – was a problem, too. Without tissue, a medical examiner has little to go on. But at death, a person’s bones start to lose water, and the proteins begin to decompose, so Busch and his colleagues chose to follow the process with moisture- and protein-sensitive diffuse reflectance near-IR. The team collected spectra from pig bones over a 3-month period. “Basically, we found that the spectra did correlate with the age [of the bones],” Busch said. “And we could make a mathematical model that we could use to determine the PMI.” The results have been promising, although Busch cautions that the work is still in the early stages. “At this point, we feel we’ve established a proof-of-concept idea,” he said. That’s the trend in forensic spectroscopy: exciting new applications of existing technology. “Near-infrared spectroscopy certainly isn’t new; people use it all the time,” Busch said. Infrared has been used to measure blood alcohol content; to analyze drug, fiber, and paint samples; and to visualize wounds such as bruises or bite marks on tissue. It also has been used to detect blood and explosives. Near-IR and Fourier transform IR have been tapped for pharmaceutical forensics as well as ink and fiber analysis. “But the funny part of it is, people who are familiar with it are often unaware of possible applications. What we try to do is see if we can come up with applications other people haven’t thought about.” Ultraviolet analysis is another crime lab standby. Many body fluids, hair types and fibers fluoresce when exposed to UV light; so do treated latent fingerprints. Albert H. Lyter III of Federal Forensic Associates Inc. in Raleigh, N.C., has used nondestructive UV and visible microspectroscopic analysis of writing inks with spectrophotometers from San Dimas, Calif.-based Craic Technologies Inc. as well as from Ocean Optics Inc. of Dunedin, Fla. “Our results indicate that the equipment is certainly more quantitative than thin-layer chromatography and provides additional information regarding ‘batch differences’ among various writing ink samples,” Lyter said. “This equipment is also much less expensive than a [gas chromatography/mass spectrometry] instrument.” Not that mass spectrometry isn’t useful in ink analysis. At Iowa State University in Ames, associate chemist Roger W. Jones is working with senior physicist John F. McClelland to apply direct analysis in real time (DART) mass spectrometry to the task. Developed by JEOL USA Inc. of Peabody, Mass., DART’s atmospheric-pressure ion source allows real-time analysis of samples in open air. Thin-layer chromatography, the traditional method of ink analysis, requires a sample of the document to be punched out with a hypodermic needle. “DART mass spectrometry is nondestructive because no pieces of the document need to be removed, and the DART method removes so little ink that the visible appearance of the document is unaltered,” Jones said. “Identification of an ink can be made by comparing its mass spectrum to a library of spectra, so no reference samples of ink are needed.” Jones and his colleagues are working on building a library. (publisher abstract modified)
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