Enantiomeric separations by capillary electrophoresis in pharmaceutical analysis

Sammanfattning: The chiral capillary electrophoresis mechanism is studied by evaluating the enantiomeric separations of a series of local anaesthetic analogues, the sixteen different optical isomers of a tetrapeptide and a series of glycyl, alanyl and leucyl dipeptides. The usefulness of mobility difference plots is appraised and important method parameters, such as the selection of the chiral selector, the chiral selector concentration, the chiral selector purity, the pH and the composition of the electrophoresis solution, are identified and discussed, bearing method robustness in mind. The evaluation of the mobility difference plots obtained for the eight enantiomer pairs of the tetrapeptide resulted in an extension of the mobility difference model. In the extended model the formation of enantiomer-chiral selector complexes with a stoichiometry higher than 1:1 is taken into account. With this model it is demonstrated that complex formation of one tetrapeptide molecule with more than one cyclodextrin molecule is a possible explanation for the experimentally obtained data.Cyclodextrins were evaluated as chiral selectors for dipeptides and have been shown to be applicable to the enantiomeric separation of aromatic and non-polar aliphatic dipeptides. By developing and validating an enantiomeric purity determination method for ropivacaine substance and products, it is shown that chiral capillary electrophoresis is a feasible technique for pharmaceutical analysis, which can offer an alternative and/or complement to chiral liquid chromatography.