Separation of enantiomers of chiral sulfoxides in high-performance liquid chromatography with cellulose-based chiral selectors using methanol and methanol-water mixtures as mobile phases

The interplay between structural details of chiral analytes and selectors in the separation of 14 chiral sulfoxides was systematically studied on 18 different polysaccharide-based chiral columns. Retention and enantioselectivity of a set of chiral sulfoxides were of primary interest. Several of chiral columns studied exhibited quite powerful chiral recognition ability in pure methanol. With addition of water to the mobile phase retention increased in the most cases and the separation factor improved. However, several exceptions were also noted. Of monosubstituted phenylcarbamates of cellulose as chiral selectors, chlorosubstituted ones did not show better enantiomer resolving ability compared to unsubstituted cellulose tris(phenylcarbamate). Out of disubstituted phenylcarbamates of cellulose the ones with methylsubstituents showed higher enantiomer resolving ability compared to chloro-substituted ones and substitution in positions 3 and 5 of the phenyl moiety was clearly advantageous. From disubstituted derivatives those possessing a combination of methyl- and chloro-substituents were advantageous compared to the ones having dimethyl- or dichloro-substituents. Interesting examples of reversal in enantiomer elution order (EEO) were observed on cellulose tris(4-chloro-3-methylphenylcarbamate)- and cellulose tris(3-chloro-4-methylphenylcarbamate)-based chiral stationary phases (CSPs) function of the water content in the mobile phase.