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Chromatography Essay

668 words - 3 pages


Chromatography is a separation technique in which the mixture to be separated is dissolved in a solvent and the resulting solution, often called the mobile phase, is then passed through or over another material, the stationary phase. The separation of the original mixture depends on how strongly each component is attracted to the stationary phase. Substances that are attracted strongly to the stationary phase will be retarded and not move alone with the mobile phase. Weakly attracted substances will move more rapidly with the mobile phase.
     Liquid chromatography is an analytical technique that is useful for separating ions or molecules that are dissolved in a liquid phase. If the sample solution is in contact with a second solid or liquid phase, the different solutes will interact with the other phase to differing degrees due to differences in adsorption, ionic strength, polarity or size. These differences allow the mixture components to be separated from each other by using these differences to determine the transit time of the solutes through a column.
     Simple liquid chromatography consists of a column with a fritted bottom that holds a stationary phase in equilibrium with a solvent. Typical stationary phases (and their interactions with solutes) are: solids (adsorption), ionic groups on a resin (ion-exchange), liquids on an inert solid support (partitioning), and porous inert particles (size exclusion). The mixture to be separated is loaded onto the top of the column followed by more solvent. The different components in the sample mixture pass through the column at different rates due to differences in their partition behavior between the mobile phase and the stationary phase. The compounds are separated by collecting aliquots of the column effluent as a function of time.
     Conventional Liquid Chromatography is most commonly used in preparative scale work to purify and isolate some components of a mixture. It’s also used in ultra trace separations where small disposable columns are used once and then discarded. Analytical separations of solutions for detection or quantification typically use more sophisticated high-pressure liquid chromatography instruments....

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