Quality by Design-Guided Development of a Capillary Electrophoresis Method for the Chiral Purity Determination of Ambrisentan

A quality by design approach utilizing experimental design methodologies was applied to develop a CE method to evaluate the enantiomeric purity of (S)-ambrisentan, a selective endothelin receptor antagonist used for the treatment of pulmonary arterial hypertension. Initial method scouting was performed by screening native cyclodextrins (CDs) as well as neutral CD derivatives and a positively charged derivative at pH 5 and pH 9, identifying γ-CD as suitable selector at pH 5. Upon defining the critical quality attributes and the critical process parameters, i.e., chiral resolution and run time, method development was performed by application of a screening design for the identification of the significant variables and, subsequently, by a response surface methodology for obtaining the design space. A Plackett–Burman design was employed for robustness testing. The final working point conditions used a background electrolyte composed of a 50-mM sodium acetate buffer, pH 4.0, containing 30 mM γ-CD in a 75-μm ID fused-silica capillary with an effective length of 40 cm at an applied voltage of 25 kV and a capillary temperature of 25 °C. The method was validated according to the ICH Q2(R1) guideline and allowed the determination of a relative concentration of the (R)-enantiomer of 0.1 %.