Dependence of the solute retention on the column pressure in reversed-phase HPLC

In the course of reversed-phase HPLC analysis, increase in pressure at the column inlet can affect the retention of sorbates only when they penetrate into the grafted phase. Due to conformational changes in the alkyl groups of the loose grafted layer, the solvation of sorbates by these alkyl groups would increase, leading to a growth of the retention factors. In the case of the surface sorption of solutes, the effect is not observed.