Abstract
The water content in mixed solvents that are used as mobile phases in liquid—solid adsorption chromatography on silica surfaces has been reported to play a special role in controlling the retention of solutes. The phenomena reported in the literature were investigated by a theoretical treatment: a priori calculations of the activity coefficients allow the influence of non-ideal mixing in the mobile phase to be estimated. Following a concept of “competitive adsorption within a multi-layer model”, the water coverage at the surface was calculated as a function of its bulk phase concentration, and the concentration range of water in the bulk phase was calculated where multi-layer adsorption of water on the surface takes place. Subtracting the influence of solute activity coefficients from measured capacity factor data, the competitive behavior of the three solvent components with respect to the solute was studied and the competitive adsorption constants were approximately evaluated by regression. Finally, the possible influence of the water content on the surface phase activity coefficients is discussed, assuming a geometric arrangement of oriented adsorbates.
Published Version
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