In contrast to analytical methods, the range of technologies currently applied for large-scale enantiomer separations is not very extensive. Therefore, a new system has been developed for large-scale enantiomer separations that can be regarded as the scale-up of a capillary electrophoresis system. In this stacked membrane system, chiral selectors that are retained by size-selective membranes are used. Upon application of an electrical potential, selective transport of the free enantiomer will occur, thus providing separation. In principle, this system can handle the same extensive range of enantiomers that can be separated in capillary electrophoresis systems on an analytical scale. In a system containing four separation compartments, alpha -cyclodextrin has been used as a chiral selector to separate D,L-Trp. Based on a transport model, a factorial design is used to investigate the effects of various process parameters. The results show that the addition of methanol is of minor influence, whereas the pH has a major effect, both on the operational selectivity and on the transport number. Experiments with AgNO3 as the background electrolyte showed that the operational selectivity has a plateau value of 1.08 at a pH ranging from 3 to 6. Because of the ease of scale-up of electrodialysis processes, this operational selectivity will allow for the separation of enantiomers on a large scale.
- chiral recognition
- racemic mixtures