DETERMINATION OF DIFFUSIVITY AND GEL CONCENTRATION IN MACROMOLECULAR SOLUTIONS BY ULTRAFILTRATION

A method is presented for determining the gel concentration and diffusivity at gelling of macromolecular solutions by comparing measured ultrafiltration limiting fluxes in plane, laminar, and turbulent channel flow with theoretical fluxes obtained from analytical mass transfer solutions. Also given is a method for determining macromolecular solution diffusivity as a function of concentration by comparing ultrafiltrate flux-pressure curves in laminar channel flow with a theoretical, closed form mass transfer solution for the flux-pressure behavior. The diffusivity of bovine serum albumin solution as a function of concentration is found at pH 4.7 (the isoelectric point) and discrepancies among existing literature values are analyzed. Gel concentration and diffusivity at pH 4.7 and 7.4 are also determined. The indirect ultrafiltration approach is shown to provide an accurate and simple means of evaluating macromolecular solution diffusivity as a function of pH, concentration, and temperature, in contrast to present sophisticated techniques that have often proved unreliable. © 1979 American Chemical Society.