Energy-dispersive x-ray spectroscopy (EDS)
Energy-dispersive X-ray spectroscopy (EDS) is an analytical technique used to identify the elemental composition of a sample by analyzing X-rays emitted from the material when it is excited, typically by an electron beam from a scanning electron microscope (SEM). This method is particularly significant in forensic science, where it helps in comparing similar items, such as metals, papers, or glasses, to determine if they share common trace elements, suggesting a shared origin. For example, EDS can help verify the authenticity of ancient coins by comparing their elemental makeup. The technique not only identifies which elements are present but also provides information on their relative proportions, crucial for distinguishing genuine items from fakes.
EDS is extensively utilized in various applications, including gunshot residue (GSR) analysis. In GSR testing, samples taken from individuals are examined for specific elements like lead, barium, and antimony, which are typically found in the residue produced when a firearm is discharged. Beyond forensic applications, EDS has also demonstrated versatility in various fields, such as uncovering forgeries and investigating the deterioration of textiles. By mapping the elemental distribution in a sample, EDS offers a powerful tool for both scientific analysis and practical applications across diverse disciplines.
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Energy-dispersive x-ray spectroscopy (EDS)
DEFINITION: Analytical technique used to construct an elemental profile of a sample of interest.
SIGNIFICANCE: Forensic scientists are often asked to compare items such as pieces of paper, glass, or metal that frequently appear quite similar under visual examination. Energy-dispersive spectroscopy is an indispensable tool under these circumstances; using this technique, analysts can determine whether particular items contain the same trace elements and establish further evidence of common origin on an atomic level.
Energy-dispersive spectroscopy (EDS) allows forensic scientists to determine which elements are present near the surface of a sample of interest and also in what approximate ratio these elements occur. This method is extremely useful for the comparison of two pieces of evidence to see if they are consistent with each other. For example, two coins, one known to be ancient and one purported to be ancient, might be compared to determine whether the second coin is a fake. EDS reveals whether the metals present in the two coins are the same or different, as well as the proportions of the metals in each coin; if the metals or their proportions are significantly different between the two coins, it may be concluded that the second coin is a fake.
The EDS instrument detects and measures the energy of X-rays that are emitted from an excited sample. When an atom is excited, it can relax in such a way that it emits X-rays with a characteristic energy for that specific element. EDS software can determine which elements are present based on the energies of the X-rays that are detected.
EDS is almost always coupled to a scanning electron microscope (SEM), which provides an electron beam to excite the sample of interest and allows an image of the surface being analyzed to be collected at the same time. If it is useful, a mapped image of the surface can be collected for various elements that shows the distribution of the elements in the area of the sample being examined.
Gunshot residue (GSR) analysis is often performed using SEM/EDS. It is known that GSR consists primarily of small, spherical particles made of lead, barium, and antimony. When a firearm is discharged, GSR plumes in all directions and deposits on the target, the surrounding area, and the hands of the shooter. In order to determine whether someone has recently fired a weapon, an analyst swabs that person’s hands and inserts the swab into the SEM with EDS detector. The SEM can be used to locate tiny spherical particles, and EDS can be performed to see which elements are present. If lead, barium, and antimony are present with no significant amount of other metals, it can be concluded that the particles are GSR.
As of 2024, SEM was used for other purposes as well, such as to identify the cause of death in a cold case as phosphorus consumption. SEM has also been used to discover forgeries and identify the cause of damage to textiles, such as clothing.
Bibliography
Bowen, Andrew, and David Stoney. "A New Method for the Removal and Analysis of Small Particles Adhering to Carpet Fiber Surfaces." Journal of Forensic Sciences 58.3 (2013): 789–96. Print.
Flegler, Stanley S., John S. Heckman, and Karen L. Klomparens. Scanning and Transmission Microscopy: An Introduction. New York: Oxford University Press, 1993.
French, James, and Ruth Morgan. "An Experimental Investigation of the Indirect Transfer and Deposition of Gunshot Residue: Further Studies Carried Out with SEM-EDX Analysis." Forensic Science International 247 (Feb. 2015): 14–17. Print.
Goldstein, Joseph, et al. Scanning Electron Microscopy and X-Ray Microanalysis. 3rd ed. New York: Kluwer Academic/Plenum, 2003.
Pilkington, Ben. "A Current View of Scanning Electron Microscopy in Forensics." AZO Materials, 25 Apr. 2022, www.azom.com/article.aspx?ArticleID=21613. Accessed 14 Aug. 2024.
Schwoeble, A. J., and David L. Exline. Current Methods in Gunshot Residue Analysis. Boca Raton, Fla.: CRC Press, 2000.
Sharma, Vishal, et al. "Applications of Energy Dispersive X-Ray Fluorescence Spectrometry and Direct Current Arc Atomic Emission Spectroscopy Methods for Grouping Study of Automobile Windshield Glasses for Glass Forensics." Chemistry Europe, 22 Mar. 2023, chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/slct.202204901. Accessed 14 Aug. 2024.