Chromatography

a method of separation based on selective adsorption. A solution of the substance is allowed to diffuse slowly through a column of adsorbent, moved by a gas or solvent flow. Different substances will pass with different speeds down the column and will eventually be separated into zones whose content may be monitored by various types of detectors. If the method is used for separation, the column core can then be pushed out and the zones of material cut apart, or the zones can be eluted by passing more solvent down the column and collecting it in small fractions.

Gas chromatographyan analytical technique for separating mixtures of volatile substances. The procedure consists of introducing the mixture to be examined into the chromatographic column and washing it down (eluting it) with an inert gas. The column is packed with adsorbent materials that selectively retard the components of the sample. A detector profiles the sample’s components, using the time each component took to reach the detector and the intensity of the detector’s response to each component.
Paper chromatographya micromethod. A drop of the liquid to be investigated is placed near one end of a strip of paper. This end is immersed in solvent that travels down the paper and distributes the materials present in the original drop selectively. Comparison with known substances makes identfication possible. The commonly used and extremely simple “blotter test” is a long-established example of the principle of paper chromatography, although it omits the solvent and standard comparison steps.
Partition chromatographyinvolves the selective solution of the desired material between two solvents. The final solvent, usually water, is used to wet the solid material packed in the column, and the first solvent containing the desired material is poured into the column as described.

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