According to stoichiometric displacement model for retention (SDM-R), the covergent phenomenon of homologues in reversed-phase liquid chromatography (RPLC) was studied. A general equation was derived for calculating the coordinates of the convergent point. The physical meaning of the coordinates was discussed from the point of view of thermodynamics. The ordinates of the two kinds of convergence are the same, i.e. the free energy change of the solutes is equal to zero. The abscissa of the concentration convergence equals to the changes in the desorbed free energy of 1mol pure organic solvent, while that of carbon number convergence equals to the negative free energy change of its end group of the homologue, when the concentration of organic solvent is one tenth in the mobile phase. The derived equation was compared with experimental data and found to fit very well.

Key words: REVERSED PHASE CHROMATOGRAPHY, LIQUID CHROMATOGRAPHY, HOMOLOG, CONVERGENCE, THERMODYNAMICS, SUBSTITUTION MEASUREMENT METHODS, FREE ENERGY