Determination of the lumped mass transfer rate coefficient by frontal analysis

The validity of measurements of the lumped mass transfer rate coefficient (km,L) is studied on the basis of experimental data acquired under Langmuir isotherm conditions, in reversed-phase liquid chromatography. Two different methods were used, the perturbation method and frontal analysis. Accurate values of km,L can be properly obtained by the perturbation method because, with this method, the chromatographic processes take place under locally linear isotherm conditions. Values of km,L can also be derived from the breakthrough curves obtained in frontal analysis. Because the contribution of axial dispersion to band broadening was larger than that of the mass transfer resistances, the apparent axial dispersion coefficient (Da) was first derived from the breakthrough curve by applying the equilibrium-dispersive model. Then, the value of km,L was calculated from Da. The values of km,L determined by the two methods were in close agreement in the range of nondimensional Langmuir equilibrium constants (r= 1/[1+KLC0]) between 0.32 and 0.85, irrespective of the mobile phase flow velocity. Thus, frontal analysis can be used for kinetic studies of the mass transfer in chromatographic columns.