DETERMINATION OF QUINIDINE, DIHYDROQUINIDINE, (3S)-3-HYDROXYQUINIDINEAND QUINIDINE N-OXIDE IN PLASMA AND URINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A specific and sensitive method for the quantitation of quinidine, (3S )-3-hydroxyquinidine, quinidine N-oxide, and dihydroquinidine in plasm a and urine has been developed. The method is based on a single-step, liquid-liquid extraction procedure, followed by isocratic reversed-pha se high-performance liquid chromatography, with fluorescence detection . After extraction from 250 mu l plasma and 100 mu l urine, the limit of determination is 10 nM and 25 nM, respectively. For the use as stan dards, commercially available quinidine was purified from dihydroquini dine; quinidine N-oxide was synthesized.