CHIRAL SEPARATIONS BY PACKED-COLUMN SUPER-CRITICAL AND SUBCRITICAL FLUID CHROMATOGRAPHY

The higher diffusivity and lower viscosity of supercritical and near-c ritical fluids can make packed-column supercritical fluid chromatograp hy or subcritical fluid chromatography (SubFC) faster with improved re solution over normal-phase HPLC for chiral separations. However, super ior fluid characteristics do not guarantee enhanced resolution or shor ter analysis time. In the case of phenylalaninol, a H-1 NMR spectrum i ndicates interaction of the solute with carbon dioxide. Such interacti on may explain the poorer resolution achieved by SubFC than by HPLC. F or a secondary amine, its H-1 NMR spectra showed no shift while poorer resolution achieved by SubFC when compared to HPLC. Thus, the NMR dat a by itself do not conclusively indicate either reaction between basic solutes and carbon dioxide or the likelihood of chiral resolution. Th e effects of column outlet pressure, organic modifier composition, pum p flow-rate and column temperature for hydroxyzine were studied. Of th e physical parameters studied, modifier composition has the greatest i mpact on retention. Increasing retention generally increases resolutio n. Changing temperature generally has less impact on retention but pro duces the greatest selectivity changes.