Electromagnetic spectrum analysis
Electromagnetic spectrum analysis is a technique used to identify substances based on their absorption of specific wavelengths of energy across the electromagnetic spectrum. This method is particularly significant in forensic science, where it aids in the analysis of unknown substances, including explosives, poisons, pharmaceuticals, and hazardous chemicals. The electromagnetic spectrum encompasses a wide range of radiation types, classified by wavelength, from radio waves to gamma rays. Of particular interest to forensic scientists is the mid-infrared region, often referred to as the "fingerprint region," which is essential for identifying unknown compounds.
In practice, infrared spectroscopy utilizes a beam of infrared radiation split between a sample of an unknown substance and a known reference sample. By measuring the energy absorbed by the samples, forensic experts can create characteristic graphs that facilitate the identification of the unknown material when compared against a database of known substances. Variations of this technique, such as Fourier transform infrared (FTIR) spectroscopy and ultraviolet spectroscopy, enhance the ability to analyze organic compounds. Notably, this method requires only small amounts of material, making it non-destructive and versatile for identifying various substances, including bodily fluids and fibers. As of the 2020s, electromagnetic spectrum analysis remains a preferred approach in forensic laboratories for its effectiveness and efficiency.
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Electromagnetic spectrum analysis
DEFINITION: Technique for identifying substances based on how they absorb specific wavelengths of energy.
SIGNIFICANCE: Forensic scientists are called upon to analyze and identify many unknown substances. Electromagnetic spectrum analysis is an important tool used in the identification of the component elements found in substances such as explosives residues, poisons, pharmaceuticals, and hazardous chemicals.
The electromagnetic spectrum is the entire range of electromagnetic radiation. Radiation is classified by wavelength, which determines the behavior of the radiation. Beginning with the longest waves, which have the lowest frequencies, the electromagnetic spectrum can be divided as follows:
- Radio waves, which are used for radio and telephone broadcasts and cellular phones
- Microwaves, which are easily absorbed by water and so are good for heating food
- Infrared radiation, which is invisible to the eye but can be detected with special infrared film
- Visible light, which is the small band of electromagnetic radiation detectable by the human eye
- Ultraviolet radiation, which causes sunburn and damage to the genetic material in cells (deoxyribonucleic acid, or DNA)
- X-rays, which pass through soft tissue and so are used in medical and forensic procedures to enable visualization of harder material such as bones
- Gamma rays, which are high-energy penetrating waves produced by radioactive material
The mid-infrared region of the electromagnetic spectrum is of most use to forensic scientists. This is sometimes called the “fingerprint region” of the spectrum because it is most useful in identifying unknown compounds. In infrared spectroscopy, a beam of a specific wavelength of infrared radiation is split, with one part passing through a sample of an unknown compound and the other through a known reference sample. A detector measures the energy of each beam after it has passed through each sample. The energy absorbed by the unknown sample is calculated through comparison of the measurements of the two beams. The amount of energy absorbed depends on the shape of the molecules in the compound. A computer manipulates the information to produce a characteristic print or graph that the forensic scientist can compare with reference graphs of known substances to identify the unknown substance.
Among the many variations on spectroscopy is Fourier transform infrared (FTIR) spectroscopy, which is often used in forensic analysis. Ultraviolet spectroscopy, which uses shorter ultraviolet light, is sometimes used to identify organic compounds. Forensic laboratories need only tiny amounts of unknown substances to identify their components using spectroscopy. In the 2020s, it was the preferred method of forensic analysis because it was not destructive and could identify a variety of materials, including bodily fluids, fibers, and hairs.
Bibliography
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 2d ed. Boca Raton, Fla.: CRC Press, 2005.
Phillips, Ken. "Spectrophotometry in Forensics." Hunter Lab, 11 Apr. 2024, www.hunterlab.com/blog/spectrophotometry-in-forensics/. Accessed 19 Aug. 2024.
Richards, Austin. Alien Vision: Exploring the Electromagnetic Spectrum with Imaging Technology. Bellingham, Wash.: SPIE Press, 2001.