SOLID-PHASE EXTRACTION-HIGH-PERFOMANCE LIQUID-CHROMATOGRAPHY DETERMINATION OF VERAPAMIL AND NORVERAPAMIL ENANTIOMERS IN URINE

A simple, rapid, sensitive and selective method has been developed for the stereospecific determination of verapamil and its metabolite, nor verapamil in urine. For sample preparation we utilized a membrane-base d solid-phase extraction (SPE) disk consisting of a thin, particle-loa ded membrane inserted in a plastic syringe-like barrel. The particles, which may be C-8 or C-18 bonded phase (C-8 in this work), are embedde d within a matrix of PTFE (Teflon) fibrils. Overall analyte recoveries were above 85%, even at low concentration of 3.0 ng/ml with reproduci bilities (C.V. values) below 13.1%. This method of extraction has the advantage of speed and considerable reduction in solvent volumes compa red to conventional SPE and solvent extraction. The separation of all the enantiomers was achieved using a single chiral stationary phase co lumn, the cellulose-based reversed-phase, Chiralcel OD-R. Analyte conc entrations of less than 3.0 ng/ml could be quantitated with C.V. value s below 14%. Calibration curves were linear in the range 2.5-300 ng/ml . Intra-day and inter-day reproducibilities were 10.5-14.2% at 3 ng/ml , 4.8-9.3% at 138.5 ng/ml and 7.8-10.1% at 280 ng/ml level, respective ly, for all the enantiomers. (C) 1998 Elsevier Science B.V.