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Applications of IR in Forensic Science

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  111

2026-06-30

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Applications of IR in Forensic Science

Because every substance absorbs radiation in the IR region of the electromagnetic spectrum, theoretically IR spectrophotometry is a practically universal technique for the analysis of evidence. There are limitations, however, on this technique that are mostly sampling related. Remember that IR analysis relies upon the presence of a pure substance. IR spectra of mixtures are difficult to interpret and are not suitable for identification. For very small amounts of impure material, purification can be impractical and IR is not used. In such cases, gas chromatography/mass spectrometry (GC/MS) is more suited. There have been attempts to marry a gas chromatograph to an IR spectrophotometer so that small amounts of material can be purified first and then analyzed. These instruments have not been very successful and have not been widely adapted to forensic use. Having said that, it is true that IR spectrophotometry is very versatile and there are a number of applications. Solid materials such as purified drugs are easily confirmed using IR. Paint samples can be ground up or analyzed by diamond cell or ATR. Liquid hydrocarbons such as gasoline can be easily characterized by IR. Plastics and other polymers can be analyzed by transmitted or reflected light.

FIGURE 5.13 A Fourier Transform Infrared Spectrophotometer with attached microscope. Small objects such as single fibers can be mounted under the microscope and high quality infrared spectra can be obtained. Note that there is no ocular to see the sample through. Instead, there is a high-resolution camera mounted on top of the microscope. This is linked to the computer which visualizes the image of the sample.