CONCENTRATION AND CONCENTRATION GRADIENT MEASUREMENTS IN AN ULTRAFILTRATION CONCENTRATION POLARIZATION LAYER .2. APPLICATION TO HYALURONAN

An optical refractometric technique has been used to acquire detailed spatially and temporally resolved concentration and concentration grad ient measurements within an ultrafiltration concentration polarization layer. Solutions containing the polymer hyaluronan (M-n=434 000; M-w= 605 000; M-z=827 000) in aqueous 10 mM NaCl and phosphate buffer solut ions were added to a dead-end ultrafiltration flow cell and solvent wa s pumped through the layer at a constant flow rate. Membrane type (hyd rophobic vs. hydrophilic track-etched polycarbonate), solvent type, in itial polymer concentration, and pumping flow rate were changed system atically to quantify the effects of these parameters on the spatial an d temporal development of the concentration polarization layer, and al so on the pressure drop across the layer. The acquired data show discr epancies with theoretical predictions based on osmotic pressure and po rous media modelling. These discrepancies may be due to a paucity of p hysico-chemical data required in the modelling, or the presence of mec hanical stresses within the polarized layer not taken into account in the theory. An improved approach for fitting polarized layer concentra tion profiles is described.