Effects of the feed solution concentration on the separation degree in Donnan dialysis for binary systems of amino acids

The separations of amino acids by Donnan dialysis using an ion-exchange mem brane were studied. Donnan dialytic experiments were carried out using an a nion-exchange membrane, glutamic acid-phenylalanine or glutamic acid-alanin e mixed solutions as the feeds, and sodium hydroxide solutions as the strip ping ones. The initial concentrations of the two kinds of amino acids in th e feed solutions were equal and in the range of 0.5-50 mol m(-3). The amino acid fluxes were measured for each feed solution. Above the feed concentra tion of 10 mol m(-3), the glutamic acid flux was over 100 times greater tha n that of the other amino acid, and it was found that the Donnan dialysis w as applicable to the separation of the amino acids. On the other hand, belo w 10 mol m(-3), the amino acid fluxes varied in a complicated manner with t he concentration, and below 1 mol m(-3) there was little difference between the fluxes of the two amino acids. Furthermore, after soaking the membrane in solutions having the same concen trations as the feed in the Donnan dialysis, uptake of the amino acids into the membrane was also measured. By comparing the experimental results of b oth the flux and uptake of the amino acids, the reason why the flux varied in a complicated manner with the concentration was discussed. (C) 2002 Else vier Science B.V. All rights reserved.