Planar Chromatography as opposed to column chromatography (e.g. GC, HPLC) utilizes a flat (planar) stationary phase for separation. In Thin-Layer Chromatography (TLC) this stationary phase is supported by a glass plate or a foil (plastic or aluminum). Again unlike column separations, the TLC plate constitutes an open system, which passes through the individual steps of the TLC analysis in an off-line mode.