Enantiomeric separation of aromatic alcohols by gas chromatography using derivatized Beta-cyclodextrins as stationary phases

Abstract

The effects of substitution types and position of 1-phenylethanol derivatives on retention and enantioselectivity have been investigated by gas chromatography using two derivatized-β-cyclodextrin stationary phases: heptakis(2,3,6-tri-O-methyl) cyclomaltoheptaose (or BMe) and heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylisilyl)cyclomaltoheptaose (or BSiMe). Thermodynamic parameters acquired by two different methods revealed that, on both columns, retention increases as molecular weight and/or polarity of substituent increases while substituent position shows little effect on retention. Contrary to retention, substituent position has a strong influence on enantioselectivity. Substantially large enantioselectivities were observed with ortho-substituted analytes of the same substituent type. Furthermore, it was found that BSiMe provided higher selectivity towards ortho-substituted analytes that BMe. This should be the influence of the tert-butyldimethylsilyl group at C6 carbons of BSiMe which results in a structural change of cyclodextrin molecule and improved selectivities.