Analysis of prostaglandin E-1 and related impurities by mixed aqueous-organic capillary electrophoresis

A capillary electrophoretic method was developed for the separation and qua ntification of prostaglandin E-1 (PGE(1), alprostadil) and its major impuri ties prostaglandin E-2 (PGE(2), dinoprostone), prostaglandin A(1) (PGA(1)), and prostaglandin B-1 (PGB(1)). The documented good stability of the studi ed analytes in organic solvents led us to try CE separation in non-aqueous media. In mixed solvents (methanol-acetonitrile), good analyte peak shapes were obtained using bile acid salts as buffer electrolytes; in particular, sodium cholate and sodium deoxycholate were found to be suitable additives when used at sub-micellar concentrations. Interestingly, the addition of wa ter to the organic running buffer permitted simultaneous improvement of the separation selectivity and the sample compatibility with the CE system. Op timisation of the experimental conditions was carried out considering the r equirements for a method devoted to analysis of impurities: precision, sele ctivity, and sensitivity (quantitation limits of 0.1%). In a fused-silica " extended path" capillary of 32.5 cm total length, the complete prostaglandi n separation was obtained in about 10 min, using 15 mM sodium deoxycholate in a mixed aqueous-organic solvent. The best separation was attained in the presence of 20% water and 80% Of Methanol-acetonitrile 75:25 (v/v). The me thod was then validated for linearity, LOD and LOQ, precision, selectivity, accuracy, and robustness; finally, it was applied to real samples, demonst rating its ability to quantify prostaglandin-related impurities.