K. Anton et al., CHIRAL SEPARATIONS BY PACKED-COLUMN SUPER-CRITICAL AND SUBCRITICAL FLUID CHROMATOGRAPHY, Journal of chromatography, 666(1-2), 1994, pp. 395-401
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.