Development and validation of LC methods for the separation of misoprostol related substances and diastereoisomers

Abstract

Misoprostol is a synthetic prostaglandin E1 analogue which is mainly used for prevention and treatment of gastric ulcers, but also for abortion due to its labour inducing effect. Misoprostol exists as a mixture of diastereoisomers (1:1) and has several related impurities owing to its instability at higher temperatures and moisture. A simple and robust reversed phase liquid chromatographic (RPLC) method is described for the separation of the related substances and a normal phase (NP) LC method for the separation of misoprostol diastereoisomers. The RPLC method was performed using an Ascentis Express C18 (150mm×4.6mm, 5μm) column kept at 35°C. The mobile phase was a gradient mixture of mobile phase A (ACN–H2O–MeOH, 28:69:3 v/v/v) and mobile phase B (ACN–H2O–MeOH, 47:50:3 v/v/v) eluted at a flow rate of 1.5mL/min. UV detection was performed at 200nm. The NPLC method was undertaken by using an XBridge bare silica (150mm×2.1mm, 3.5μm) column at 35°C. The mobile phase contained 1-propanol–heptane–TFA (4:96:0.1%, v/v/v), pumped at a flow rate of 0.5mL/min. UV detection was performed at 205nm. This LC method can properly separate the two diastereoisomers (Rs>2) within an analysis time of less than 20min. Both methods were validated according to the ICH guidelines. Furthermore, these new LC methods have been successfully applied for purity control and diastereoisomers ratio determination of misoprostol bulk drug, tablets and dispersion.