Liquid chromatographic determination of quinidine in serum and urine.

A liquid chromatography method for the determination quinidine in serum and urine has been developed. This method uses isocratic conditions, ambient temperature, a conventional fixed wavelength, 254-nm detector, and is free of potential interference from quinidine metabolites. Sample pretreatment involves extraction of quinidine along with quinine, an internal standard, into an organic phase and reextraction into an aqueous acidic phase. In this manner, interference due to commonly used drugs are eliminated. The method is capable of accurately measuring quinidine to levels as low as 0.5 mg/L.