A pressure-driven separation process, using self-supporting crosslinked sodium alginate (SA) membranes with different swelling indices, enabled the optical resolution of a-amino acids, including the optical isomers of tryptophan and tyrosine. The SA membranes were prepared by the casting and drying of SA solutions on an acryl plate, followed by crosslinking with glutaraldehyde. They were characterized with analytical methods, such as Fourier transform infrared and swelling index measurements. During optical resolution with the SA membranes, the effects of experimental factors were studied, such as the concentration of the feed solutions, the operating pressure, and the degree of crosslinking of the membranes. When an SA membrane with a swelling index of 80% was used, a good optical resolution of tryptophan isomers was obtained: an enantiomeric excess of 54.0% and a flux of 24.8 mg/m(2) h. (C) 2003 Wiley Periodicals, Inc.