Quantitative Analysis of Sodium Valproate in Pharmaceutical Preparations by a Valproate-Selective Electrode

A simple and rapid method for the determination of sodium valproate in pharmaceutical preparations, without prior separation, has been developed using a valproate-selective electrode. A plastic liquid membrane electrode kit was used for the electrode based on the use of valproate : methyltris(tetradecyl)ammonium ion-pair complex in n-decanol and polyvinyl chloride matrix. The electrode showed a near-Nernstian response in the range of 10-2 to 2×10-4M sodium valproate. Life span of the electrode was at least 1 month. The electrode was also used fot the determination of the pKa of valproic acid. Determination of 90 to 1500μg/ml of sodium valproate in aqueous solution showed an average recovery of 100.0% (mean standard deviation 0.4%) by direct potentiometry. Pharmaceutical excipients and diluents commonly used in drug formations did not interfere with the analysis. The selectivity of the electrode to some inorganic and organic anions was described. This assay was applied to determine sodium valproate in pharmaceutical preparations and the results compared favorably with those obtained by gas chromatography.