Thin-layer chromatography involves the equilibration of a compound between a mobile phase and a thin (e.g., 0.25 mm) stationary phase bonded to a at plate (usually glass). The mixture is applied in a volatile solvent, and the plate is developed with a suitable mixture of solvents. The mobility of each component is measured with respect to the solvent front, and the ratio of the distance moved by the compound to that of the solvent front, the “Rf,” should be constant for a given combination of stationary and mobile phases.