HPLC DETERMINATION OF VERAPAMIL AND NORVERAPAMIL IN PLASMA USING AUTOMATED SOLID-PHASE EXTRACTION FOR SAMPLE PREPARATION AND FLUOROMETRIC DETECTION

A sensitive and fully automated method for the simultaneous determinat ion of verapamil and its main metabolite norverapamil in plasma is des cribed, which involves the solid phase extraction (SPE) of the analyte s from plasma on disposable extraction cartridges (DECs) and reversed phase HPLC with fluorescence detection. The DEC filled with endcapped cyanopropyl silica (50 mg) was first conditioned with methanol and pho sphate buffer of pH 7.4. A 1.0-mL volume of plasma sample containing t he internal standard was then applied on the DEC. The washing step was performed with the same buffer. The analytes were eluted with 0.24 mt of methanol containing 0.2 % of 2-aminoheptane. A 0.41-mt volume of a cetate buffer of pH 3.0 was then passed through the DEC and 0.25 mt of the resultant extract was directly introduced into the HPLC system. T he absolute recoveries of the drugs were around 95 % and the limit of detection of verapamil was 1.0 ng/mL. The within-day and between-day r eproducibilities at a plasma concentration of 100 ng/mL were 1.4 % and 1.9 %, respectively.