Thin-layer chromatography: a neglected technique.

Thin-layer (or planar) chromatography (TLC) is critically reviewed from the point of view of drug analysis in biological fluids. The capabilities of the various techniques of TLC are described and their advantages and disadvantages are discussed. An example of the use of high-performance TLC with scanning densitometry for the quantitative determination of antipyrine in human plasma is provided. The use of TLC-mass spectrometry and TLC-tandem mass spectrometry, directly from the sorbent, in the identification of the compounds separated by TLC is discussed.