In thin-layer chromatography or TLC, analytes mixed with the mobile solvent travel through a thin layer of polar silica or alumina gel by capillary action.

The analytes are spotted on the lower part of the plate in microgram quantities such that the top of the mobile phase is below the bottom of the spots so that it moves evenly up the plate.

The characteristic affinity of an analyte for a set of chromatographic conditions is expressed as the retardation factor, R_f, which is the distance traveled by the solute divided by the total distance traveled by the mobile phase.

TLC separates a sample mixture into distinct spots by moving components at different rates across the stationary phase, each characterized by its specific R_f value.

So, it can be used to predict whether a given set of chromatographic conditions will adequately separate the analytes in a mixture.

TLC is also used to predict separation in column chromatography and identify unknown compounds by matching their R_f values to known compounds.