Micellar electrokinetic chromatography as a fast screening method for the determination of 1,4-dihydropyridine calcium antagonists

A micellar electrokinetic chromatographic method (MEKC) was optimized for the separation of six calcium antagonists. The effects of the buffer (concentration and pH), concentration of sodium dodecyl sulphate (SDS), the organic modifier, the injection time, and the voltage applied were studied. A final appropriate electrolyte of 50 mM borate buffer, pH 8.2, containing 20 mM SDS and 15% (v/v) acetonitrile was found to provide the optimum separation with respect to resolution and migration time. The samples were introduced hydrostatically for 4 s at 50 mbar injection pressure and the applied voltage was +25 kV. The screening of the six compounds was achieved in less than 15 min: nifedipine (migration time, tm = 6.9 min), nimodipine (tm = 10.1 min), felodipine (tm = 12.2 min), nicardipine hydrochloride (tm = 12.7 min), lacidipine (tm = 13.5 min) and amlodipine besylate (tm = 14.1 min, tm = 8 min). The method developed showed to be linear at least up to 70 micrograms/ml with a detection limit of about 5 micrograms/ml for each compound. The within-day and inter-day area reproducibility (R.S.D.) were, respectively, lower than 4.8 and 8.6% for six replicate samples.