Chromatography is a laboratory process used to separate mixtures by the absorbency of their individual components, according to Princeton University's WordNet Search. There are many forms, including paper, thin-layer and column chromatography. One type of column chromatography is High Performance Liquid Chromatography (HPLC).
HPLC is often used to identify an unknown mixture by determining its organic chemical components. It is also used to remove impurities from a single-component substance.
The heart of HPLC equipment is a column, usually made of glass. A small part of an unknown mixture is usually injected by syringe through a membrane at the top of the column.
The mixture's components travel along the column at different rates, which separates them. A detector indicates when they leave the column, and a recorder charts the results.
A HPLC column is packed with a fine-grained, absorbent solid -- such as aluminum and other metallic oxides -- called the "stationary phase." A mobile, "liquid phase" is pumped through the stationary phase, dissolving the unknown mixture and moving its components along. The stationary phase absorbs and slows the liquid phase. The mixture's components respond differently, causing them to separate.
The separated components can be analyzed further by other laboratory methods, including infrared spectroscopy.