Large-scale gradient elution chromatography

Yung-Huoy Truei, Purdue University

Abstract

The goal of this thesis work is to provide practical strategies for large scale separations by gradient elution chromatography. A detailed model was used for gradient elution systems considering interference effects, longitudinal diffusion, film mass transfer, intraparticle diffusion, mixing mechanism of the mobile phases, and Langmuir-type adsorption and desorption kinetics. This detailed model can be solved by an efficient and robust numerical procedure. All the input parameters in this model have been either experimentally measured or estimated through empirical correlations. Hence, the optimization strategy of gradient elution has been developed using this detailed model. The detailed model used here can quantitatively predict experimental band positions, with a relative error of less than 5%, at various gradient concentrations, gradient periods, flowrates, and column lengths. Qualitative agreement between experimental and numerical results is similarly obtained for the band widths and profiles. As a result of optimization, an optimal column length may exist. The pore size distribution of the stationary phase is important for the intraparticle diffusion of macromolecules. For the chromatographic material used here, the manufacturer has reported a narrow pore size distribution on the basis of pore volume, with a mean pore size of 300 A. It is shown that it is preferable to report the pore size distribution in terms of surface area, upon which the distribution broadens, and the mean size becomes 50 A. An alternative instrument for large-scale production using gradient elution has been suggested and compared with conventional gradient elution instrumentation. This instrument design is cost effective and can avoid the problems of air bubbles and inaccurate flowrate of the pump. The tolerance of gradient elution processes to the fluctuation of input parameters has also been discussed. Displacement chromatography, a stepwise gradient chromatographic method, has been experimentally compared with conventional gradient elution chromatography. In the case of crossing isotherms, displacement chromatography can be successful, even though it is commonly believed that it will fail. The isotherms expressed in units of moles rather than mass, and in terms of the occupied ratio of stationary phase, should be used for the interpretation of affinity or displacement sequence in displacement chromatography.

Degree

Ph.D.

Advisors

Tsao, Purdue University.

Subject Area

Chemical engineering

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