Evaluation of a rapid gas-chromatographic method for the simultaneous quantitative determination of ethosuximide, phenyletheylmalonediamide, carbamazepine, phenobarbital, primidone and diphenylhydantoin in human serum.

A simple and rapid gas chromatographic method for the simultaneous estimation of the anticonvulsant drugs ethosuximide, carbamazepine, phenobarbital, primidone, diphenylhydantoin and the metabolite PEMA in serum is presented. The method is based on a simple ether extraction of 1 ml serum before and after precipitation of the proteins by ammonium sulfate and injection of the extract dissolved in methanol without derivative formation. Gas chromatographic separation is performed on a highly polar acidic phase (SP 1000, a terephthalic acid modified Carbowax 20 M), for detection the instrument is equipped with a nitrogen selective detector, quantitation is performed by automatic electronic integration of peak areas in relation to the internal standard Mesantoin. The optimal approach to the gas chromatographic analysis of "problem drugs" like carbamazepine and phenobarbital is discussed, various stationary phases and support materials are compared for effectiveness with this method. In the analysis of over 800 routine serum samples as well as internal and external quality control samples this method was found to be reliable and the results reproducible.