Enantiomeric resolution study by capillary electrophoresis. Selection of the appropriate chiral selector

The enantiomeric separation of several arylpropionic acids, namely carprofen, cicloprofen, flurbiprofen, ibuprofen, indoprofen, ketoprofen, naproxen and suprofen has been studied by capillary zone electrophoresis using different chiral selectors added to the background electrolyte with the aim to find the optimum experimental conditions for both qualitative and quantitative purposes. The chiral selectors used included two ?- cyclodextrin derivatives and a glycosidic antibiotic, namely 2,3,6-tri-O- methyl-?-CD, heptamethylamino-?-CD and vancomycin. When the CDs were used the chiral selector was present in both capillary and electrode compartments while for vancomycin the partial filling method was used (the chiral selector was not present at the detector window in order to improve the sensitivity; vancomycin is strongly absorbing at low wavelengths). Enantiomeric resolution was recorded for all the compounds studied except for ibuprofen when heptamethylamino-?-CD was used; resolution generally increased by increasing the chiral selector concentration. Good sensitivity and good precision for both migration times and corrected peak areas (A(sample)/migration time) were achieved using the three chiral selectors. Among the three chiral additives employed vancomycin proved to be the most effective for the enantiomeric separation of the studied arylpropionic acids. The optimized method achieved analysis with the shortest time (<6 min), and the highest efficiency (270 000 plates x meters).