Thin-Layer (Planar) Chromatography

Synthetic dyes comprise a large group of organic, organic salt and organometallic compounds which number in the thousands. Most individual dyes are assigned colour index (CI) numbers which helps to identify structure and properties as well as identity where a series of names have been used by the manufacturers for the same dye. Pigments are also listed and can be either organic or inorganic in nature. The value of planar chromatography in the identiRcation of dyes and separation of impurities and their quantiRcation is the main subject of this article. Synthetic dyes will be split into nine groups, the Rrst three being the major ones. For all these groups, the development of modern thin-layer chromatographic (TLC) methods will be compared where possible with older TLC procedures.