Effect of selector coverage and mobile phase composition on enantiomeric separations with ristocetin A chiral stationary phases

Three different amounts (i.e., selector coverages) of ristocetin A macrocyc lic antibiotic have been covalently bonded to silica gel, packed in stainle ss steel columns, and evaluated as chiral stationary phases (CSPs) in high- performance liquid chromatography (HPLC). The three columns (i.e., CSPs) we re examined and compared in the reversed-phase, polar-organic, and normal-p hase modes. The retention behavior (k'), selectivity (alpha), resolution (R -s), and number of theoretical plates (N) fur all three columns are discuss ed and compared in each mobile phase mode. The coverage of the chiral selec tor had a profound effect on the chromatographic behavior of the more retai ned enantiomers. A special mobile phase composition (i.e., methanol plus ve ry small amounts of acid and base modifiers) resulted in improved baseline separations, without greatly affecting the analysis times, for all chiral a nalytes evaluated. The column stabilities were excellent when switching bet ween different mobile phase modes. (C) 1999 Academic Press.