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Applications of UV/Visible Spectroscopy in Forensic Science

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  104

2026-06-29

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Applications of UV/Visible Spectroscopy in Forensic Science

One major application of this type of spectroscopy is the determination of the exact color of an object or substance. The paint chip described previously is an example of when this would be needed. UV/visible spectroscopy is also widely used in the analysis of textile fibers. See Chapter 15 for a discussion on textile fibers. A microspectrophotometer can be employed to compare the colors of two fibers. In a murder case that occurred in Michigan more than 20 years ago, purple fibers were transferred from a sweater worn by the victim to the seat of a car driven by the suspected killer. Samples taken from the sweater were compared to those lifted from the car seat and the exact colors were determined. Microspectrophotometry has also been used for determining the color characteristics of hair dyes. The same hair dyes were put on different color hairs and the colors were compared to see if the natural color of the hair affected the dye color. Another experiment determined if the color of the dyes changed with time. Microspectrophotometry has also been widely used to compare plastic fragments from the covers on lights on cars. Sometimes it is important to obtain the ultraviolet spectrum of objects of evidence that are colorless. One example is automobile paint clear coats. A clear coat is the top, colorless layer of coating that is applied to automobile paints to protect the color coats from exposure to the sun’s ultraviolet light. The clear coat contains UV “scavengers”—chemicals that absorb large quantities of UV light. Different paint manufacturers use different chemical formulations in their clear coats. The ultraviolet spectrum of the clear coat can be important in associating paint chips from an incident scene to a suspect automobile. Colorless plastic items such as certain automobile light covers, plastic bags used to transport drugs and plastic films can also be analyzed by ultraviolet spectroscopy. Powder forms of illicit drugs are generally white and have no visible spectrum but might have a characteristic ultraviolet spectrum. This is illustrated in Figure 5.5, the ultraviolet spectrum of heroin. UV/visible spectrophotometry can also be used to determine the amount of a sub stance in a mixture. This is because of its adherence to Beer’s Law. This law relates the amount of an absorbing substance present to the quantity of absorbed light. The absorbance can be obtained directly from the spectrum of the substance. It is related to the height of the absorbance peak. In general, the concentration of a UV/visible absorber is directly proportional to its absorbance. So if heroin is dissolved in a sol vent that doesn’t absorb UV light, the concentration of the heroin can be determined from the UV spectrum.