Method for diphenylhydantoin and phenobarbital assay by gas chromatography

A rapid and easy method for determination of diphenylhydantoin and phenobarbital in plasma by gas liquid chromatography which provides monitoring of epileptic patients therapy is described. These drugs are extracted from plasma by partitioning between cholroform and buffered aqueous phase. The final extract is evaporated to dryness and the residue dissolved in an internal standard (methaqualone) solution. An amount of the final extract is injected tnto OV1 3% column at 230degreeC without previous derivative formation. The results are compared to those obtained by thin layer chromatography followed by colorimetry.