Capillary gas chromatographic assay for valproic acid and its 2-desaturated metabolite in brain and plasma

A capillary gas chromatographic method has been developed for quantitating the antiepileptic drug valproic acid and its pharmacologically active metabolite, E-delta 2-valproic acid, in brain and plasma. The method was designed to cover large concentration ranges of both valproic acid and E-delta 2-valproic acid for pharmacokinetic and pharmacodynamic studies in laboratory animals and human subjects. Careful optimization of the extraction and chromatographic procedures was needed to resolve the analytes from a variety of endogenous constituents and other known metabolites of valproic acid. A sensitivity limit of 0.10 micrograms/g for 300 mg of brain tissue or 0.20 micrograms/ml for 150 microliters of plasma was achieved using flame ionization detection. The within-batch coefficients of variation for both analytes were less than 8%. Reproducible calibration data were observed over a period of three to eleven months.