n. [ Gr. &unr_;, &unr_;, color + -graphy. ] 1. A treatise on colors [ archaic ] [ 1913 Webster ]

2. (Chem.) an analytical and preparative technique for separating substances by differences in their selective adsorption to solids, by passing a liquid over the solid, to which the substances to be separated have usually been adsorbed in a preliminary step. The major variations are column chromatography, in which the substances to be separated are adsorbed to a column with any of a wide variety of adsorbing solids in powdered or granulated form; paper chromatography, in which the solids are applied as a spot at one end of a strip of absorbent paper (such as filter paper), and the liquid is percolated through the paper by capillary action; and thin-layer chromatography (TLC), which is similar to paper chromatography, but the adsorbent material is, instead of paper, a thin layer of finely powdered material, such as cellulose or silica, on a backing of glass or plastic, called a TLC plate. A modern version of column chromatography is high-performance liquid chromatography, usually referred to as HPLC. [ PJC ]