Chromatographic separation of (E)- and (Z)-isomers of entacapone and their simultaneous quantitation in human plasma by LC-ESI-MS/MS.

A selective, sensitive and high throughput liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for the chromatographic separation and quantitation of (E)-entacapone and (Z)-entacapone in human plasma. Sample clean-up involved liquid-liquid extraction (LLE) of both the isomers and carbamazepine used as internal standard from 500microL of human plasma. Both the analytes were chromatographically separated with a resolution factor of 3.