Application of multisolute adsorption equilibrium to the simulation of nonlinear chromatographic band profiles

In this study, multisolute adsorption equilibrium data were determined experimentally for three systems which are relevant to the area of preparative liquid chromatography. The first system refers to the multisolute adsorption of three light aromatic alcohols on a reversed phase column from a mobile phase composed of a mixture of water and methanol. The second system corresponds to the adsorption of three basic drugs on a C18 column from a buffered mixture of water and acetonitrile. The third system refers to the adsorption of a racemic pharmaceutical intermediate on a chiral column from acetonitrile.

A nonideal, adsorbed solution theory model was developed in order to better understand the distribution of the phenylalcohols between the adsorbed and the bulk phases. The model is able to accurately predict the competitive data based on the single solute adsorption data. It was found that the activity coefficients of the solutes in both phases at equilibrium are roughly constant. In our opinion, this fact explains why the competitive adsorption data presented in this and previous studies can be successfully predicted using simple models like the Langmuir, bi-Langmuir or the ideal adsorbed solution theory models.

Finally, high-concentration band profiles and system peaks were also measured for the aforementioned experimental systems. Theoretical band profiles were calculated using the relevant adsorption isotherms and the equilibrium-dispersive model of nonlinear chromatography. Very good agreement was found between the experimental and the calculated band profiles. This fact provides additional evidence about the usefulness of the equilibrium-dispersive model for the method development, scale-up and optimization of preparative separations when using highly efficient columns.