Development and validation of a cyclodextrin‐modified capillary electrophoresis method for the enantiomeric separation of vildagliptin enantiomers

The enantiomers of vildagliptin, an orally available and selective dipeptidyl‐peptidase‐4 inhibitor used for the treatment of type II diabetes, have been separated by CD‐modified CZE, using uncoated fused‐silica capillary. After screening 13 negatively charged CD derivatives as potential chiral selectors, sulfobutyl‐ether‐α‐CD (SBE‐α‐CD) was selected for the enantioseparation. For the optimization, a factorial analysis study was performed by orthogonal experimental design. Six experimental factors were chosen as variable parameters: temperature, applied voltage, chiral selector and BGE concentrations, pH, and the parameters of the hydrodynamic injection. The optimized system still was not considered final as the second peak (S‐enantiomer) migrated too close to the EOF, resulting in a potential inaccuracy during the determination of the chiral impurity. To fine‐tune the method “one factor at a time” variation approach was applied. The final method (applying 15°C capillary temperature, 40 mbar × 4 s hydrodynamic injection, 25 kV voltage in 75 mM acetate‐Tris buffer pH 4.75] containing 20 mM SBE‐α‐CD as chiral selector) was validated according to the ICH guideline. RSD percentage of the resolution value, migration times, and corrected peak areas were below 5% during testing repeatability and intermediate precision. LOD and LOQ values were found to be 2.5 and 7.5 μg/mL, respectively. The method is considered linear in the 7.5–180 μg/mL range for the R‐enantiomer. The robustness of the method was justified using Plackett–Burmann statistical experimental design.