Ultraviolet spectrophotometry
Ultraviolet spectrophotometry is an analytical chemistry technique primarily utilized for screening chemical compounds by measuring the light absorbed in the ultraviolet spectral region. This sensitive, nondestructive method is particularly significant in forensic science, where it aids in the preliminary identification of classes of compounds, such as drugs, explosives, and toxic substances. Although it cannot confirm specific compounds due to limited specificity, UV spectrophotometry is adept at revealing the presence of aromatic or conjugated structures typical in many controlled substances.
In forensic applications, it provides valuable quantitative data, allowing scientists to compare the concentration of substances in suspected tampered samples against known standards. Its capabilities extend to analyzing paints, soils, and even deoxyribonucleic acid (DNA). For more detailed structural analysis, UV spectrophotometry is often complemented by other techniques, such as infrared spectroscopy or mass spectrometry. Additionally, advancements like microspectrophotometry enable the analysis of small samples, enhancing its utility in various investigative contexts. This technique continues to evolve, with recent innovations such as dual-comb spectroscopy improving its applicability in low light conditions.
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Ultraviolet spectrophotometry
DEFINITION: Analytical chemistry technique used as a screening tool in classifying chemical compounds.
SIGNIFICANCE: Forensic scientists often use ultraviolet spectrophotometry when conducting preliminary screening to identify classes of compounds, such as in drug screening, detection of explosives, toxicology, paint analysis, and soil discrimination.
Ultraviolet (UV) spectrophotometry is a nondestructive, sensitive technique that measures light absorbed by a sample in the ultraviolet spectral region. UV spectrophotometry has two general uses in forensics: screening and quantitation. Although not useful as a confirmatory test, UV spectrophotometry is a good preliminary screening method to identify classes of organic compounds with aromatic rings or conjugated systems. These structural features are common in many types of drugs and other controlled substances and in many materials used in explosives.
UV spectrophotometry can be used as a screening tool to identify a class or group of compounds in a sample. Although scientists can determine the presence or absence of suspected compounds using this technique, UV spectrophotometry has limited specificity because structurally related compounds can generate similar spectra. Many compounds, including various drug groups, produce characteristic spectra, but these spectra typically do not provide enough detail for specific compound identification; they are most useful for determining a class of compounds present in a sample. UV spectrophotometry is thus most useful for single-component analysis of samples with known or suspected composition, such as pharmaceuticals.
Different compounds have varying capacities to absorb UV light, so mixtures of compounds can complicate analysis. For example, a compound that absorbs UV light strongly combined with a that is a weak UV absorber may generate a spectrum that masks the presence of the controlled substance. Specific compound identification requires more precise chemical analytical tools that can provide structural detail, such as infrared (IR) spectroscopy or (MS).
UV spectrophotometry can also be used to quantify a substance in a sample. The amount of UV light absorbed by a sample corresponds to the concentration of a particular substance in the sample. A forensic scientist can use such a quantitative procedure, for instance, to compare the concentration of a substance in a sample that is suspected of being tampered with to the concentration of the same substance in a known, unaltered sample. These measurements can be followed with more thorough analyses using other techniques to determine the actual concentration and identity of the substance in question.
UV spectrophotometry can be used to identify controlled substances and drugs of abuse, such as and methamphetamine. This technique can also be used to detect compounds that might be found in explosives, such as compounds that contain nitro groups attached to aromatic rings. Forensic scientists also use UV spectrophotometry in analyzing soils and paints as well as in quantifying (deoxyribonucleic acid). For analysis of small samples, UV spectrophotometry can be combined with a microscope in the technique known as microspectrophotometry. In 2024, researchers advanced the practice of dual-comb spectroscopy, making it more suitable for low light intensities.
Bibliography
Bell, Suzanne. Forensic Chemistry. Upper Saddle River, N.J.: Pearson Prentice Hall, 2006.
"Breakthrough in Ultraviolet Spectroscopy." ScienceDaily, 15 Mar. 2024, www.sciencedaily.com/releases/2024/03/240315160951.htm. Accessed 19 Aug. 2024.
Houck, Max M., and Jay A. Siegel. Fundamentals of Forensic Science. Burlington, Mass.: Elsevier Academic Press, 2006.
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.
Silva, Marcela Fernandes, et al. "Usability of Simplified UV-Vis Spectrophotometric Methods for the Determination of Nitrate in the Presence of Organic Matter and Chloride as Interfering Factors." Water Practice and Technology, 2024, doi.org/10.2166/wpt.2024.043. Accesed 19 Aug. 2024.