Simultaneous isothermal determination of diphenylhydantoin and phenobarbital serum levels by gas-liquid chromatography following flash-heater hexylation.

A rapid, accurate, precise, and sensitive procedure for the simultaneous determination of diphenylhydantoin and phenobarbital under isothermal conditions involves on-column hexylation of the compounds. After extraction of serum samples, the evaporated residues are dissolved in tetrahexylammonium hydroxide. An aliquot of the resulting solution is introduced directly into a gas chromatograph where conversion to hexyl derivatives and subsequent separation takes place. The hexylated derivatives are identified by their retention times relative to appropriate internal standards. Concentrations are obtained from standard curves plotting relative peak height versus concentration of drug.