Interference phenomena and rate equation model of multicomponent ion exchange chromatography
Abstract
A theory has been developed to describe the ion exchange equilibria of biochemicals with pH, salt, and opposite charge effects. Cation exchange equilibrium properties of eight typical amino acids were obtained with batch experiments and analyzed with the theory developed. The deprotonated $\alpha$-carboxyl groups of amino acids of amino acids inhibit the bindings of $\alpha$-amino groups drastically. The apparent affinities are strong functions of pH and the bindings of amino acids are heterogeneous. For example, basic amino acids undergo monovalent cation exchange at high pH and divalent cation exchange at low pH. The equilibrium parameters obtained were also used in simulating fixed-bed dynamics of amino acid separations. The Interference Theory has been used to elucidate the interference phenomena of multicomponent ion exchange chromatography with multiple step inputs, two-way flow, and pH gradients. A rate equation theory, which accounts for axial dispersion, film mass transfer, intraparticle diffusion, size exclusion, and nonlinear isotherms, has been developed to simulate the dynamics of multicomponent adsorption and ion exchange. The model equations were solved with a new method of orthogonal collocation on gradient-directed moving finite elements which adjusts both the number of finite elements and their boundaries to focus the collocation points to the steep concentration gradients. The computation time for the step change simulation was reduced to 1/5th of that of orthogonal collocation on fixed finite elements. Extensive computer simulations based on the Interference Theory have been carried out. The simulation results elucidate the interference phenomena of various fixed-bed processes, which include frontal analysis, elution, displacement, selective displacement, countercurrent regeneration, two-way and pH gradient elution, and pH gradient focusing. The non-linearity of concentrated systems and the interference effects of concentration on affinity sequences have also been studied and the rate equation model has then been used to simulate the mass transfer effects. Fixed-bed experiments of amino acid and protein separations were in good agreement with the corresponding predictions. The understanding and simulations of multicomponent ion exchange dynamics provide important guidelines for the design and optimization of chromatographical processes.
Degree
Ph.D.
Advisors
Wang, Purdue University.
Subject Area
Chemical engineering|Analytical chemistry
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