COMBINED EFFECTS OF FINITE AXIAL-DISPERSION AND SLOW ADSORPTION DESORPTION-KINETICS ON BAND PROFILES IN NONLINEAR CHROMATOGRAPHY

The analytical solutions of the Thomas model derived by Goldstein and Wade et al. are compared to numerical solutions of the Thomas and the reaction-diffusive models. The latter model includes the axial dispersion, neglected in the Thomas model, as well as the kinetics of the reaction mechanism. The solutions of the two models converge when the contribution of the axial dispersion becomes small compared to that of the reaction kinetics. However, when the mass-transfer kinetics is the rate-determining step or when the rates of the mass transfer and the reaction kinetics are of the same order, important differences between the solutions of the two models are observed. If the kinetics of the retention mechanism is very slow and the split peak phenomenon takes place, numerical solutions of either model predict the entire band profile while the analytical solutions of the Thomas model remain unable to predict the profile of the unretained part of the split peak.