Determination of phenobarbital, ethosuximide, and primidone in human serum by micellar electrokinetic capillary chromatography with direct sample injection.

The determination of antiepileptic drugs in human serum by micellar electrokinetic capillary chromatography (MECC) with direct sample injection is discussed. Nanoliter quantities of patient sera are applied to the beginning of a fused silica capillary filled with a phosphate/borate buffer (pH 9.2) containing 75 mM sodium dodecylsulfate. Upon application of an electric field along the capillary, endogenous and drug substances are transported toward the cathode and separate into distinct zones which are detected by on-column UV absorption. Phenobarbital, ethosuximide, and primidone are shown to elute in front of the solubilized proteins, thus permitting quantitation of these drugs without any sample pretreatment. For phenobarbital and ethosuximide, MECC data obtained using the external standard method and peak areas as the basis for quantitation are shown to be in excellent agreement with those of nonisotopic immunoassays and, for ethosuximide, also with those of high-performance liquid chromatography. The correlation coefficients (n = 50) are between 0.972 and 0.986. Intraday and interday reproducibility data are 2.0-4.5% and 4.5-8.0%, respectively. For primidone, insufficient samples have been available for a comprehensive comparison of MECC data with those of other analytic techniques.