Two expressions of calculating entropy changes △S~(~P~a~) solute either with, or without column phase ratio in reversed-phase liquid chromatography were theoretically derived. The latter is also an equation to express the quantitative relationship between some linear parameters in stoichiometric displacement model for retention (SDM-R) and the thermodynamic functions in the same process. The △S~(~P~a~), liking Gibbs free energy and enthalpy changes, can also be divided into two independent fractions, adsorption entropy change, △S~(~Ⅰ~,~a~) and desorption entropy △S~(~Z~,~D~). Based on the quantitative relationship between the solute retention and the activity of displacing agent in mobile phase described by te SDM-R, the △S~(~P~a~), △S~(~Ⅰ~,~a~) and △S~(~Z~,~D~) under various a~D can be evaluated, respectively. The experimental and the evaluated results of entropy were obtained with a good agreement. The traditionally qualitative rule that adsorption of component is companied with the decrease in entropy, on a contrary, desorption is that with the increase in it can be quantitatively elucidated with the studies.

Key words: ADSORPTION, RETENTION, SOLUTE, DESORPTION, RP-HPLC