SELECTIVE SEPARATION OF AMINO-ACIDS WITH A CHARGED INORGANIC NANOFILTRATION MEMBRANE - EFFECT OF PHYSICOCHEMICAL PARAMETERS ON SELECTIVITY

A charged organic-inorganic nanofiltration (NF) membrane prototype was used to separate a mixture of nine amino acids (AA) on the basis of d ifferential electrostatic interactions with the membrane because, for a given pH, some of them were positively charged, some were negative, and some were zwitterions. Effect of pH, amino acid concentration (C-r ), and added ionic strength ([NaCl]) on the process selectivity was st udied. A global statistical study revealed that pH was the dominant pa rameter regarding fractionation. C-r and [NaCl] had a weaker effect, b ut the ratio C-r/[NaCl] demonstrated a pronounced effect on system sel ectivity. Two split-ups of the mixture were obtained at pH 2 and at pH 12, for a 1-g/L total AA concentration and a C-r/[NaCl] ratio of 0.16 . Under these conditions, the differences in transmissions between bas ic and acid AA were higher than 70%. Interpretation of the results acc ording to the Donnan theory allows us to foresee the potentialities of charged nanofiltration membranes for the fractionation of a complex m ixture, such as peptidic hydrolysate to streams containing peptides an d amino acids having different isoelectric points. (C) 1997 John Wiley & Sons, Inc.