No abstract

The adsorption isotherms of bovine serum albumin (BSA) on TOSOHAAS TSK-GEL DEAE-5PW were determined in a pH ) 7.5 buffer for a 1.0 mL/min flow rate and at pH ) 6.0 for 1.0, 2.0, and 3.0 mL/min flow rates. The isotherm data were derived from the breakthrough curves obtained by step series frontal analysis (FA) method. The sample concentrations ranged from ca. 0.2 to 3 mg/mL. From the Scatchard plots, it was found that the bi-Langmuir isotherm model fits the adsorption isotherm data better than the single Langmuir isotherm model at both pH ) 7.5 and 6.0, for flow rates up to 2.0 mL/min. The rate of the mass transfer kinetics was determined for each breakthrough curve by using a lumped kinetic model. An average rate coefficient of mass transfer kinetics was derived. This rate coefficient depends linearly on the average sample concentration.

The extension of the shock layer theory to systems having a slow mass transfer kinetics and a concentration-dependent rate coefficient is discussed. Experiments were carried out with bovine serum albumin on two anion exchangers, TSK-GEL-DEAE-5PW and Resource-Q. The adsorption isotherm data, determined by single-step frontal analysis, could be fitted to simplified bi-Langmuir equations with very small residuals. A lumped kinetic model (solid film linear driving force model, with rate coefficient k f ) was used to account for the mass transfer kinetics. The profile of each breakthrough curve (BC) was fitted to the curve calculated with this transport model and the rate coefficient k f obtained by identification. A linear dependence of k f on the average concentration of the step of the BC was found. The shock layer thicknesses (SLT) calculated for different relative concentrations agreed very well with the experimental results. This justifies the use of the SLT for the direct determination of rate coefficients.