Development of Stereoselective Method for the Quantification of Stereoisomers and Geometrical Isomer of Pitavastatin Calcium by Enhanced Approach

A new, simple, selective, and robust normal-phase method for the accurate quantification of all the four stereoisomers and one geometrical isomer of pitavastatin calcium (PIT) in drug substances and drug products was developed. The method is capable of quantifying all the isomers in the presence of other related substances. Separation was achieved using immobilized amylose stationary phase (Chiralpak IA) with a mixture of n-heptane, 1-butanol, methanol, formic acid, and diethylamine. Multivariate analysis and statistical tools were used to develop this highly robust method in a short span of time. A central composite design was employed to study the main effects and interactions of the independent variables. The method exhibited consistent, high-quality recoveries [97.3 ± 1.7 to 99.3 ± 2.1 (mean ± RSD)] with a high precision for all the isomers. Linear regression analysis revealed an excellent correlation between peak responses and concentrations (r 2 values of 0.9990–0.9998) for the isomers. The method is sensitive enough to quantify any isomers above 0.02 % and detect any isomer above 0.006 % in PIT. Forced degradation studies proved that the method is specific for isomers. m/z values were determined for the major degradants and their possible structures were proposed on the basis of the known reactivity.