Chromatography
Chromatography is a laboratory technique employed to separate chemical mixtures into their individual components, enabling the identification and quantification of these isolated substances. Developed in 1903 by Russian botanist Mikhail Semyonovich Tsvet, the name "chromatography" derives from Greek words meaning "color writing," reflecting its initial application in separating plant pigments. The process involves a sample dissolved in a mobile phase—either a liquid or gas—that interacts with a stationary phase, usually a solid or liquid. This interaction causes different components of the mixture to migrate at varying rates based on their physical properties, facilitating separation.
Chromatography plays a significant role in forensic science, helping determine causes of death, linking individuals to crime scenes, and analyzing residues from explosives. Its applications extend to detecting substances in airport baggage, identifying drugs, and analyzing biological samples for toxins. Techniques such as liquid and gas chromatography utilize columns through which the mobile phase flows, often incorporating detectors to analyze the components as they are released. Overall, chromatography is essential in various scientific fields, providing critical information for legal and safety investigations.
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Chromatography
DEFINITION: Laboratory techniques used to separate chemical mixtures into their individual components and to quantify and identify the isolated components.
SIGNIFICANCE: Chromatography techniques are useful for a variety of purposes in the forensic sciences, including determining causes of death, linking individuals to specific crime scenes, and analyzing the residues from explosives to identify possible suspects.
Chromatography was invented in 1903 by the Russian botanist Mikhail Semyonovich Tsvet, who used it to separate plant pigments, the various colored components of plants such as chlorophyll, carotenes, and xanthophylls. It has been suggested that Tsvet arrived at the name “chromatography” for this process by combining the Greek words chroma and graphein, literally meaning “color writing.” The uses of chromatography are not limited to colored substances, however.
The various forms of chromatography all share certain characteristics. For example, the sample to be analyzed is dissolved in a mobile phase, typically a liquid or a gas, which then comes into contact with a stationary phase, typically a solid or a liquid. As the mobile phase flows over the stationary phase, the various components of the sample are attracted to each phase to different extents, based on their physical characteristics. Those components that are attracted more to the stationary phase will move less quickly than those that are attracted more to the mobile phase, so the components separate from each other.
Chromatographic techniques may be categorized based on the nature of the mobile phase. In liquid chromatography, the mobile phase is a liquid. In gas chromatography, the mobile phase is a gas. Additionally, many of these techniques use columns containing the stationary phase; the mobile phase flows through the column after the sample has been dissolved in the mobile phase and applied to the column. When the components of the chemical mixture have been separated, they may be identified through the use of a detector attached to the chromatographic system. The detector, which may include one of several instruments used in chemical analysis, records various physical properties of the components. When a column is used, the detector is attached to the end of the column where the components are released. This method, known as column chromatography, is the most commonly used method.
Chromatography is used in the forensic sciences whenever it is necessary to separate the chemical components of a sample to determine the identity or the quantity of one or more of those components. The uses of chromatography include detecting the presence of explosives in airport baggage, analyzing explosives residues to identify the sources as well as possible suspects, and determining cause of death in autopsies through the screening of biological samples (such as blood, hair, and skin) for drugs or poisons. Chromatography is also used to identify the chemical makeup of seized illicit drugs and to determine blood alcohol levels in persons accused of driving under the influence of alcohol. Using chromatography techniques, analysts can determine the composition and quantity of the dyes in textile fibers left at a crime scene and thus help identify the potential source of the fibers, examine the ink on legal documents to determine whether any information has been fraudulently inserted, compare small amounts of soil to link suspects to a crime scene, determine the likely factory source of automobile paint left at the scene of a hit-and-run accident, detect the presence of accelerants at the scene of an arson investigation, and screen foods to determine whether they have been contaminated with dangerous chemicals.
Bibliography
Bogusz, M. J., ed. Handbook of Analytical Separations. Forensic Science, vol. 6. Ed. Roger M. Smith. 2nd ed. New York: Elsevier, 2007. Print.
Dettmer-Wilde, Katja, and Werner Engewald. Practical Gas Chromatography: A Comprehensive Reference. New York: Springer, 2014. Print.
Fanali, Salvatore, Paul Haddad, Colin Poole, Peter Schoenmakers, and David Lloyd. Liquid Chromatography: Applications. Waltham: Elsevier, 2013. Print.
Miller, James M. Chromatography: Concepts and Contrasts. 2nd ed. Hoboken: Wiley, 2009. Print.
Premnath, Sujatha Mahadevarao, and Muhammad Zubair. "Chromatography." StatPearls, 11 Jan. 2024, www.ncbi.nlm.nih.gov/books/NBK599545/. Accessed 14 Aug. 2024.
Wixom, Robert L., and Charles W. Gehrke, eds. Chromatography: A Science of Discovery. Wiley, 2011.