Column chromatography
Column chromatography is a versatile analytical technique used to separate complex mixtures into individual components, facilitating the identification and quantification of various chemical species. It is particularly significant in forensic science, where analyzing intricate samples can yield critical information about their constituents, potentially linking samples to common sources. The method involves a stationary phase, typically composed of particles packed within a column, through which a mobile phase—either gas or liquid—flows, enabling the separation of components based on their unique properties.
Within column chromatography, two prominent subtypes are gas chromatography (GC) and high-performance liquid chromatography (HPLC). GC is often employed in forensic investigations, such as arson cases, utilizing long, narrow columns that allow for precise temperature control to analyze gases. In contrast, HPLC operates under high pressure and is utilized for analyzing a diverse array of substances, including illegal drugs and poisoning agents, with columns made of durable materials like stainless steel. Additionally, solid phase extraction (SPE) serves as a specialized application of column chromatography for sample preparation, effectively concentrating specific compounds, such as illicit drugs from biological samples. Overall, column chromatography plays a crucial role in chemical analysis, providing valuable insights across various fields.
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Column chromatography
DEFINITION: Technique used to analyze complex samples by separating the mixture of chemical species into individual components so their identities and concentrations can be determined.
SIGNIFICANCE: Forensic samples can be complex mixtures of components, and determination of the individual components in a sample may provide investigators with valuable information. The components, once separated, are normally evaluated by a detector that is able to determine specific chemical or physical information about each component. The similarity between samples or the likelihood that samples have a common origin may be determined after individual components are evaluated.
Column chromatography is one of the subtypes of chromatography. The term “column chromatography” is applied to a variety of techniques that can be classified by the phase of the material that is moving through the column. When this mobile phase is a gas, the technique is called gas chromatography (GC); when the phase is a liquid, it is called liquid chromatography. The column can be filled with particles, which is called a stationary phase, that allow a separation of individual components to take place. Instrumentation is often used to push the mobile phase through the column at higher pressures, allowing faster and improved separation of components.
Capillary GC is a common technique that requires that chemical components be analyzed in their gas state. It uses narrow glass columns that can be as long as 100 meters (roughly 330 feet). The insides of the columns can be coated with different chemical polymers so different types of chemical species can be separated. These columns are coiled for easy placement in an oven so the temperature can be controlled accurately. By changing the temperature, the scientist can analyze different chemical species. GC is commonly used to analyze samples taken from fire scenes in arson investigations.
High-performance liquid chromatography (HPLC) is a widely used analysis technique that employs high-pressure pumps to force a liquid phase through columns packed with small particles. Columns come in a variety of sizes, with inside dimensions smaller than 0.10 millimeters (0.004 inches) to as large as a few centimeters. To handle the high pressure, the columns are commonly made of stainless steel, but they may be made out of plastic for specific applications such as ion chromatography. Solvents such as methanol and water are commonly used as mobile phases. HPLC can be used to separate and analyze a range of forensically important samples; it is commonly used to determine the presence of illegal drugs and to determine what substances were used in suspected poisonings.
Solid phase extraction (SPE) is a specific type of column chromatography designed for sample preparation. It uses plastic columns filled with particles specifically designed to either attract or ignore different chemical compounds that would be found in a sample. For example, it can be used to concentrate illicit drugs from urine.
Bibliography
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Telepchak, Michael. Forensic and Clinical Applications of Solid Phase Extraction. Totowa: Humana, 2004. Print.