When the mobile phase along with the mixture that needs to be separated is introduced from the top of the column, the movement of the individual components of the mixture is at different rates. The components with lower adsorption and affinity to stationary phase travel faster when compared to the greater adsorption and affinity with the stationary phase. The components that move fast are removed first whereas the components that move slowly are eluted out last.
The adsorption of solute molecules to the column occurs in a reversible manner. The rate of the movement of the components is expressed as:
Rf = the distance travelled by solute/ the distance travelled by the solvent
Rf is the retardation factor.