Simulation of multicomponent elution with the mobile phase containing competing modifiers

Abstract

In elution chromatography, modifiers sometimes are added to the mobile phase to compete with sample solutes for binding sites in order to reduce the retention time and band spreading of sample solutes. In this work, the interrelationship between modifiers and sample solutes in preparative and large-scale chromatography is investigated using a nonlinear multicomponent rate model in which axial dispersion, film mass transfer, intraparticle diffusion, and multicomponent Langmuir isotherm are considered. The modifier with a constant concentration in the feed mobile phase is treated as one of the components in the governing equations of the model and is included in the multicomponent Langmuir isotherm. Peaks that are directly attributed to the modifier in the chromatogram are termed system peaks. It has been concluded that for an elution system with two sample solutes and one modifier, there exist three different patterns of system peaks if the sample contains the modifier, and six if the sample does not contain the modifier. It has been found that apart from the thermodynamic effects, the dispersion and mass transfer effects, in some cases, also play important roles in determining system peak patterns. Simulations for an elution system with two modifiers have also been investigated and discussed.