Abstract
Enantioseparations of phenothiazines with γ‐cyclodextrin (γ‐CD) as a chiral selector were investigated using citrate and phosphate buffer electrolytes at pH 3.0. Reversal of the enantiomer migration order of promethazine, ethopropazine, and trimeprazine was observed by varying γ‐CD concentration in the range of 5–9 mM, 2.5–4.5 mM and 1.5–2.8 mM, respectively, using 100 mM citrate buffer at pH 3.0. As in the case of β‐CD, the (+)‐enantiomers of phenothiazines possess greater binding strength to γ‐CD than the (−)‐enantiomers. The evaluation of the binding constants and limiting mobility of the complexes formed between the enantiomers of phenothiazines and γ‐CD reveals that the binding strength of phenothiazines to γ‐CD and the differences in the binding constants and limiting mobility of the complexes are responsible for the enantiomer migration reversal. Both the binding constants and limiting mobility of the complexes between the (+)‐enantiomers of phenothiazine and γ‐CD are greater than those of the corresponding (−)‐enantiomers in a citrate buffer, while the binding constants of the complexes primarily determined the migration order of the enantiomers in a phosphate buffer. Compared with the results obtained using a phosphate buffer, we may conclude that citrate buffer which involves competitive complexation with chiral selector plays a significant role in the enantiomer migration reversal.