Abstract: In consideration of the adsorption of solvent, diluent and solute molecules on the surface of a stationary phase, a new equation for solute retention in liquid chromatography is presented. This equation includes three parameters: the displacement equilibrium constant(K_sd) between the solvent and diluent molecules on the surface of the stationary phase, the total number(N) of the solvent and diluent molecules released from the stationary phase after one solute molecule being adsorbed, and the parameter(I) related to the thermodynamic equilibrium constant for the solute adsorption on the stationary phase. Over the whole concentration range of the solvent in the mobile phase, the experimental retention data can be well described by this equation, parameters K_sd, N and I can be obtained by the regression analysis of the experimental retention data, and consequently the number of the solvent and the diluent molecules displaced by one solute molecule from the stationary phase can also be derived at different solvent concentrations in the mobile phase.

Key words: Liquid chromatography, Retention equation, Retention parameter