ENANTIOMER SEPARATION BY CAPILLARY SFC AND GC ON CHIRASIL-NICKEL - OBSERVATION OF UNUSUAL PEAK BROADENING PHENOMENA

Immobilized chirasil-nickel (nickel(II) (heptafluorobutanoyl)-(1R)-10- methylenecamphorate] chemically bonded to a poly(dimethylsiloxane)) wa s employed for the separation of enantiomers by capillary supercritica l fluid chromatography and gas chromatography. In SFC, the dependence of the retention behavior (k') and chiral separation factors (alpha) o n applied pressure, density, and analysis temperature has been investi gated for the two representative chiral test solute 1-phenylethanol an d camphor. Even at high densities of the carbon dioxide mobile phase, the enantioselectivities measured at low temperatures under supercriti cal conditions were found to be similar to those expected from the ext rapolation of high-temperature measurements in GC. Systematic variatio ns in temperature or pressure in SFC resulted in unusual enantioselect ive peak-broadening phenomena, which were observed independently from the enantiomeric purity of the solutes. These phenomena were amplified substantially both under overload conditions and at reduced mobile-ph ase flow rates.