Theory of electrochemically modulated liquid chromatography

A theoretical treatment based on models developed to describe the adsorption features of solutes at electrified interfaces is presented for the interpretation of the retention characteristics of solutes when electrochemically modulated liquid chromatography is used. The treatment is general, covering all possible compositions of the mobile phase. A number of limiting cases with practical interest is examined in detail. It is shown that the treatment can give a molecular explanation of the experimental results. According to the theoretical predictions, the dependence of the logarithm of the capacity factor, ln k′, upon the applied potential, Eappl, is affected decisively by the composition of the mobile phase. In particular, the shape of the ln k′ versus Eappl curves depends upon the presence or not of specifically adsorbed ions, the presence or not of organic modifiers and their molecular properties. The shape of these curves may be linear or quadratic over a limiting range of potentials, as found in several experimental studies, depending on the presence or not of an organic modifier in the mobile phase and the dielectric properties of the adsorbed species on the stationary phase.