Based on the stoichiometric displacement model for retention in liquid chromatography, two linear relations for the plots of lgI (constant relating to the affinity of 1mol solute to stationary phase) and Z (moles of displacing agent released as 1mol solute is adsorbed versus reciprocal of absolute temperature) in reversed-phase high preformance liquid chromatography (RP-HPLC) were theoretically derived, respectively. It was found that both lgI and Z of both apolar and polar small solutes have the characters of thermodynamical equilibrium constant. The total enthalpy during retention process of solute, as the same instance as that of Gibbs free energy reported in the previous paper, can also be divided into two independent fractions, adsorption and desorption enthalpy changes which can be used to evaluate both △H(Pa) and △H(Z,D) with various concentrations of displacing agent in mobile phase. With the comparisons between the experimental and the evaluated results, the standard deviation was found to be less than ±10%. The changes in heat during retention process in RP-HPLC were also explained with the magnitudes of the △H(1,a) and the △H(Z,D).

Key words: HIGH SPEED LIQUID CHROMATOGRAPHY, ADSORPTION, REVERSED PHASE CHROMATOGRAPHY, ENTHALPY, ANALYTIC