Mixed-solvent theory for liquid chromatography

Abstract

The competitive- and solution-interaction models are further developed. Certain assumptions previously made in the theory are shown to be either unacceptable or unnecessary. It is shown that both the Langmuir and diachoric-solution models lead to an equation relating inverse retention volume in a simple manner with volume-fraction composition of the mixed solvent. Results are presented for elution of several solutes from carbon tetrachloride + diethyl ether mixtures over the whole range φ= 0–1. This provides the first data covering the whole concentration range.

Although the same general equation describes both theoretical approaches, it is shown how they may be distinguished in the light of experiment. It is concluded that all data so far published fall into a group in which over the approximate range φ= 0.1–1, there is no competitive adsorption of the solvent components and the diachoric model applies. The importance of extending studies over the range φ= 0–1 is emphasised as also is the need to work with solvent pairs capable of competitive adsorption over a wider range of φ.