Determination of verapamil by adsorptive stripping voltammetry in urine and pharmaceutical formulations.

A sensitive reduction peak of verapamil is obtained by adsorptive stripping voltammetry in 0.01 M phosphate (pH 7.4) at an accumulation time of 30 s. The peak potential is -1.81 V (vs. Ag/AgCl). The peak current is directly proportional to the concentration of verapamil (1x10(-8)-1x10(-6) M), with a 3sigma detection limit of 5x10(-10) M (0.246 ng/ml). The R.S.D. at the 1x10(-7) M level is 1.8%. The interference of some metal ions, and some amino acids, and the application of the method to analysis of urine, and pharmaceutical formulations are described. The method is simple (no extraction), rapid (30 s accumulation time), sensitive (the detection limit of verapamil is 0.491 ng/ml), reproducible(within day R.S.D. of 1.28-1.8%), and suitable for routine analysis of verapamil, urine, and pharmaceutical formulation.

Adsorptive stripping voltammetric determination of antihypertensive agent: diltiazem.

Adsorptive stripping voltammetry was used to determine the antihypertensive agent diltiazem in phosphate buffer (pH 7.0). The adsorptive cathodic peak was observed at -1.72 V vs. Ag/AgCl. The peak response was characterized with respect to pH, preconcentration time, possible interferences, accumulation potential and supporting electrolytes. The obtained results were analyzed and the statistical parameters were calculated. The proposed method was applied to determine the mentioned drug in pharmaceutical formulation (capsule) and urine. The detection limit is 1x10(-8) M (4.5 ng ml(-1)) using 180 s preconcentration time, whereas the lower limit of detection is 6x10(-9) M (2.7 ng ml(-1)).

pH-metric studies on ternary metal complexes of some amino acids and benzimidazole.

The stability constants of binary and ternary complexes of copper(II) and nickel(II) with some amino acids (d-histidine, dl-serine, lysine) as primary ligands and benzimidazole as a secondary ligand were determined pH-metrically. The study was conducted in 10% (v/v) ethanol-H(2)O medium and at an ionic strength of 0.1 mol dm(-3) NaNO(3) at 20 +/- 1 degrees C, Values of Delta log K were discussed on the basis of statistical considerations and the nature of the species formed. The stability of the binary and mixed ligand complexes are discussed in terms of the molecular structure of benzimidazole and the amino acids as well as the nature of the metal ion.