AXIAL-DISPERSION IN A MAGNETICALLY STABILIZED FLUIDIZED-BED LIQUID-CHROMATOGRAPHY COLUMN

Interest in the magnetically stabilized fluidized bed as a bioprocessing tool has developed rapidly in recent years. While several demonstrations of bioseparations in the MSFB already have been published, little information about the basic characteristics of this system as a new chromatographic tool have yet emerged. We investigated the axial dispersion characteristics of laboratory-scale MSFB columns loaded with 95-mu-m support particles, a size appropriate for chromatography. Dispersion coefficients determined for inert tracer injections at flow rates up to 4 times the minimum fluidization velocity for the bed were of the same order of magnitude as those in packed beds. At still higher velocities, dispersion coefficients were an order of magnitude greater than those found in packed beds. The MSFB was even more susceptible to nonuniformities of fluid distribution than ordinary fluidized beds, because magnetic particle aggregation tended to exacerbate flaws spontaneously appearing in the bed. Though horizontal field stabilization required higher field strengths, this orientation seemed somewhat more resistant to growth of flow nonuniformities. In these batch bed studies, we found plate counts of between 1000 and 6000 plates/metre, corresponding to dimensionless HETPs of 2 to 10 particle diameters, in 1/4- and 3/8-in diameter columns.