Separation and Determination of Stereoisomeric Impurity of Folinic Acid Diastereomers by CE with Vancomycin as a Selector

A highly sensitive and rapid method was developed that involves capillary electrophoresis for separation and determination of the stereoisomeric impurity of folinic acid diastereomers. In this method, vancomycin was used as the chiral selector, and a solution of poly(dimethylacrylamide) (PDMA) was prepared for dynamic coating of the capillary wall to minimize the adsorption of vancomycin. This method was optimized for six factors including concentrations of the organic modifier and vancomycin, pH and concentration of the background electrolyte, column temperature, and separation voltage. The following conditions were established: 100 mM Tris-phosphate buffer (pH 6.0) containing 1.0 mM vancomycin and 5 % acetonitrile at 30 °C, and −15 kV applied voltage on the PDMA dynamically coated capillary. Preliminary validation was performed with the determination of limit of quantification and detection, accuracy, precision, and linearity. Under our optimized method, the folinic acid diastereomers were baseline-separated within 7.5 min, and a (6S,2′S)-calcium folinate sample with 0.08 % stereoisomeric impurity was determined.