Chromatography is a way to separate single chemical compounds from mixed substances that depends on the speed at which they move through special media, or chemical substances. It consists of a stationary phase (a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase. Chromatography is much used in biochemistry and analytical chemistry.
Column Chromatography [change]
Column chromatography separates compounds using many chemical actions between the chemical being tested and the chromatography column (a rod with a blending of special chemicals). The column is run using either gravity or a pump.
The mixed substance to be tested is added in a small amount and is slowed by certain chemical or physical activity with the chemicals in the chromatography column. The amount of slowing depends on the type of chemicals in the substance being tested and the different phases. The time at which a certain chemical elutes (comes out of the end of the column) is called the "retention time" and there is thought to be only one for one chemical.
The most common stationary phase for column chromatography is silica gel, followed by alumina. Cellulose powder has been much used in the past. The mobile phase is either a pure solvent or a mixture of solvents. It is chosen make the time and amount of solvent used as little as possible, while still clearly separating the chemicals being tested.