Extraction-spectrophotometric determination of phenytoin in capsules and plasma using potassium permanganate/dicyclohexano-24-crown-8

An extraction-spectrophotometric method for the determination of phenytoin in capsules and plasma is presented. The method is based upon oxidation of phenytoin using alkaline potassium permanganate solubilized in chloroform/cyclohexane (1:1) after crowning with dicyclohexano-24-crown-8 (DC-24-C-8). The formed benzophenone being soluble in the oxidation reaction medium was directly measured at 238 nm. The optimum conditions for the reaction were studied and the detection limit was found to equal 1.2 mg/100 ml. The developed method was applied to the determination of the drug in capsules and plasma. The method is simple, accurate and avoids laborious multistep extraction procedures.