Swelling of dextran gel and osmotic pressure of soluble dextran in the presence of salts

The swelling of dextran gels (Sephadex) in salt solutions with a water acti vity of 0.937, compared with the swelling in pure water, exhibited anion sp ecificity as evidenced by an increased swelling ratio in the following orde r: Na2SO4 < H2O < NaCl < NaSCN. The swelling ratio showed a good linear cor relation with the osmotic pressure of dextran (500 kD) in these solutions. The salt-concentration difference (imbalance) between the polymer-solution side of the membrane and the polymer-free permeate side during the osmotic- pressure measurements positively correlated with the effect of the salt on the polymer osmotic pressure. These phenomena conform to Hofmeister-type (o r lyotropic) behavior. The diminishing augmentation of dextran osmotic pres sure and the change in the salt-concentration imbalance with rising NaSCN c oncentration imply a positive preferential interaction and adsorption of th e salt onto the polymer. (C) 2001 John Wiley & Sons, Inc.