Gas chromatographic determination of verapamil in plasma and urine

A gas-liquid chromatographic method for the determination of verapamil in body fluids has been developed. Verapamil and internal standard are extracted from alkalized fluid with heptane and then back extracted into 1 N HCl. After re-extraction into heptane, verapamil and internal standard are analysed by gas-liquid chromatography using a nitrogen-specific detector (N-FID). The method is specific for verapamil. Concentrations can be measured down to 4 ng ml-1 plasma. The coefficients of variation in plasma samples were 5--8% (within-day; range of concentration 5--30 ng ml-1). Recovery in this range was 100 +/- 6.2% during several weeks.