A Kinetic Study on the Mass Transfer Phenomena in Reversed-Phase Liquid Chromatography

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Kinetic studies on the mass transfer phenomena in columns were studied by means of pulse response experiments and the moment analysis under the conditions of reversed-phase liquid chromatography (RPLC). Various stationary phases having different physical and chemical properties were used, that is, porous silica gel particles bonded with alkyl chains of different carbon numbers, porous silica gel particles bonded with C_<18>-ligands of different surface coverages, porous silica gel particles bonded with phenyl group, porous particles made of styrene-divinylbenzene copolymer, and porous particles made of graphitic carbon. Methanol/water mixtures and standard materials of benzene derivatives and phenol derivatives were mainly used as the mobile phases and sample compounds, respectively. The information about the retention equilibrium and mass transfer kinetics were derived from the first absolute moment and the second central moment of the elution peak profiles. Especially, the characteri … More stics and mechanism of surface diffusion were studied in detail. To the best of the author's knowledge, there is so far no systematic study on surface diffusion. Thermodynamic properties of the retention equilibrium and surface diffusion were derived from the results of the pulse response experiments carried out under different temperature conditions. It was tried to systematically analyze the results in this study from various points of view in order to consistently understand the separation mechanism in RPLC.On the basis of the results about surface diffusion, the surface-restricted molecular diffusion model was proposed for surface diffusion as a first approximation. The new model was formulated according to the absolute rate theory. This model is effective for a comprehensive interpretation of the intrinsic characteristics and mechanism of surface diffusion.New moment equations were derived for monolithic columns packed with continuous porous separation media by solving the basic equations of the general rate model of chromatography in the Laplace domain. They correlate the peak moments and some parameters characterizing the retention equilibrium and the mass transfer kinetics in monolithic columns. Some items of new information on the mass transfer kinetics in C_<18>-silica monolithic columns were derived by applying the new moment equations to a set of experimental data. The validity of the new moment equations was confirmed. Less