Objective To establish a sensitive and selective LC/MS/MS method for the determination of phenytoin in healthy human plasma to study on the bioequivalence of different formulations containing phenytoin. Methods Phenytoin and the internal standard osalmid were extracted from plasma with liquid - liquid extraction, then separated on a Zorbax SB -C18 column. The mobile phase consisted of methanol -water -formic acid (90: 10: 0. 2) , at a flow - rate of 0. 6 mL · min-1. A Finnigan TSQ quantum ultra tandem mass ...