Tuesday, May 13, 2008

It will not surprise anyone at microscopes.com that chromatography was first invented by a Russian. He was separating plant pigments, which is why separation methods are called "Chromo" tography. Imagine a group of people are going out on the town. They're in a town with many different types of entertainment. As they walk down the street some of the people go into the theatre, some go into the comedy club, and some go to the casino. They are separating themselves by their different affinities (tastes). In the same way chemicals are carried along by a mobile phase (liquid or gas) past a stationary phase (gel, or silica, or chemical bonded on particles) and separate themselves by their affinity for the stationary phase. Eventually they are all replaced on the stationary phase by the mobile phase. They are carried past a detector in separate bands in the mobile phase. The chemicals can be detected in various ways the most common is by their absorption of a specific wavelength of light (UV detection). The amount of light absorption is directly proportional to the chemical's concentration. The different types of chromatography are categorized by their stationary phase or by the mobile phase in the case of Gas Chromatography (GC). Thin Layer Chromatography (TLC) is a stationary phase thinly coated on an inert support plate. Liquid Chromatography (LC) is small particles coated with the stationary phase and packed into a column. High Performance Liquid Chromatography (HPLC) is similar to LC except that the particles are much smaller and the analysis is performed under high pressures. Other types of chromatography include Ion Exange Chromatography which separates molecules by their charge and Size Exclusion Chromatography (SEC) which separates large molecules like proteins by their size.