Based on thermodynamical standpoint, a new definition of column phase ratio in reversed-phase high performance liquid chromatography (RP-HPLC) and its determination method are presented. The contribution of the column phase ratio defined in this paper was found to be comparable to the Gibbs free energy change of solute during stoichiometric displacement process. The Gibbs free energy change of solute △G~(Pα) during chromatogrpahic process may be divided into two independent fractions expressing adsorption and desorption free energy changes △G~(Ⅰ,α) and △G~(Z,D), due to the stoichiometric displacement model for retention of solute. Both △G~(Ⅰ,α) and △G~(Z,D) under different compositions of mobile phase may be evaluated with equations derived in this paper. Compared to the experimental results, the relative deviation of the expected one's is generally lower than ±2%.

Key words: ADSORPTION, THERMODYNAMICS, REVERSED PHASE CHROMATOGRAPHY, DESORPTION, GIBBS FREE ENERGY