Obtaining the concentration-dependent diffusion coefficient from ultrafiltration experiments: Application to hyaluronate

A method for determining the concentration-dependent mutual diffusion coefficient D(C) of a macromolecule-solvent combination over a wide macromolecular concentration range is presented. All necessary data are gathered from a single experiment, in which polymer concentration profiles are measured during one-dimensional dead-end ultrafiltration. Based on these profiles, the convection-diffusion equation is used to deduce the dependence of D on C. To demonstrate the utility of the approach, studies using sodium hyaluronate dissolved in either 10 mM NaCl or a phosphate buffer were carried out. For hyaluronate (HA) in 10 mM NaCl, the mutual diffusion coefficient varies approximately linearly with concentration according to D(C) = 4.1 X 10(-6) C-0.96 cm(2)/s in the range 0 less than or equal to C less than or equal to 0.6 mass %, for C expressed in mass %. However, transition points (slope changes) in the D(C) curve are present at C approximate to 0.7 mass % and C approximate to 1.4 mass %. For HA in the phosphate buffer, the mutual diffusion coefficient is well described by D(C) = 1.9 X 10(-6) C-0.825, for 0 less than or equal to C less than or equal to 1.8 mass %. These values agree well with previously published data. The technique is robust, and permits reasonably high polymer concentrations to be easily studied. (C) 1996 John Wiley & Sons, Inc.