Measurement of verapamil concentrations in plasma by gas chromatography and high pressure liquid chromatography

This study was carried out to compare gas chromatography (GC) and high-pressure liquid chromatography (HPLC) procedures in the measurement of plasma levels of verapamil. Other analytic methods previously reported are not widely available (mass fragmentography) or are subject to interference from drug metabolites (spectrophotofluorometry). A single extraction and derivatization procedure was developed to prepare samples for either GC or HPLC analysis. The GC procedure used a nitrogen-specific detector; the HPLC, a fluorescence detector. In a 1--500 ng/ml range of verapamil concentrations, both methods resulted in good separation of verapamil from a major metabolite, norverapamil, and from compound D517, used as an internal standard. Intraassay variation was similar for both procedures, with only slightly higher interassay variability found for the GC technique. Excellent correlation was found during analysis of the same unknown samples by both methods (r = 0.97; p less than 0.001). Either assay procedure appears satisfactory for use in measurement of verapamil levels in plasma.