Principle: TLC is based on the differences in affinity of a compound between the mobile phase and the stationary phase, leading to a separation of the different compounds of a mixture.

This difference in affinity can be assimilated to a partition constant K of the compound between the mobile phase and the stationary phase:

The partitioning operation is REPEATED a great number of times, CONTINUOUSLY, thus making it possible to exploit even minimal differences in affinity: each compound of the sample moves at its own speed behind the solvent front.