Determination of nifedipine in human plasma by capillary gas chromatography with nitrogen detection.

A gas chromatographic method for the determination of nifedipine in human plasma is presented. Nifedipine was extracted from plasma at basic pH with toluene, and nitrendipine was used as the internal standard. Chromatography was performed on a cross-linked methylsilicone fused-silica column by on-column injection and with a nitrogen-phosphorus ionization detector. The minimal detectable concentration was approximately equal to 0.5 ng/ml of plasma. The standard curve was linear in the range evaluated, 2-300 ng/ml plasma. The within-analysis coefficient of variation was 3.9-10.4%, and the day-to-day coefficient of variation was 3.8%. A peak with the same retention time as the nitropyridine derivative of nifedipine was detected in the plasma of patients who had taken 10 mg nifedipine orally.