A high performance liquid chromatographic method is presented for the determination of verapamil and its metabolite norverapamil in human plasma. Verapamil and norverapamil are extracted from plasma basified with 0.5M dibasic sodium phosphate (pH 9.5) using ethyl acetate containing trimipramine as an internal standard. A reverse-phase cyanopropylsilane column was used with a mobile phase of 65 acetonitrile and 35 0.02M acetate buffer (pH 7.0). The minimum detectable limit was 2 ng/ml of plasma. The effect of the pH, molarity, and percent acetonitrile of the mobile phase on the capacity factor was studied. Possible interferences from other drugs administered concurrently are presented.
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