A common method for the determination of several calcium channel blockers using an HPLC system with ultraviolet detection

We report a common HPLC method for the single or simultaneous determination of four calcium channel blockers (CCB), namely diltiazem (DTZ), verapamil (VER), nifedipine (NIF) and nitrendipine (NIT) and their active metabolites demetildiltiazem and deacetildiltiazem (MA and M1), norverapamil (NOR), an d dehydronifedipine (DHN). DHN was first synthesised in our laboratory and different pH values of the mobil phase were subsequently prepared and teste d for chromatographic separation. The detection system and the environmenta l light conditions were optimised. The best separations of all analytes wer e obtained using a C-18 column and a mobile phase of methanol, 0.04 M ammon ium acetate, acetonitrile and triethylamine (2:2:1:0.04 v/v). Quantitation was performed using imipramine (IMI) as the internal standard. For DTZ and its metabolites (M1 and MA), the wavelength chosen was 237 nm; for VER and its metabolite NOR, it was 210 nm; and, finally for NIF and its metabolite DHN and NIT it was 216 nm. When a simultaneous analysis was carried out the wavelength was of 230 nm. The optimum pH were 7.90 and 7.10 when the separ ation of NIT and DTZ or VER and NIF were carried out, respectively, and 7.9 0 when a simultaneous separation was carried out. The detection limit of th e assay was less than 8 ng ml(-1) for all compounds, with coefficients of v ariation less than 7% (for inter- and intra-day) over the concentration ran ge of 1-1000 ng ml(-1). The retention times were less than 11 min. When NIF or NIT were studied, it was necessary to use a sodium vapour lamp in order to avoid the photodegradation which takes place under daylight conditions. (C) 1998 Elsevier Science B.V. All rights reserved.