Spectrophotometric Determination of Captopril and Penicillamine through the Use of Ligand Exchange Complexation Reactions.

Two spectrophotmetric methods based on combined redox - ligand exchange reactions were developed for the determination of captopril and penicillamine in pure form and in their dosage forms. The first method is based on attenuating the absorbance of a ternary complex: silver (I) - bromopyrogallol red - phenanthroline in a buffer solution of pH6-8. The method has the concentration ranges 2-10 μg mL(-1) and 0.5-1.75 μg mL(-1) for captopril and penicillamine respectively, and the detection limits 7.1 × 10(-2) and 5.7 × 10(-2) μg mL(-1) for captopril and penicillamine respectively. The second method is based on decreasing the absorbance of a chloroformic solution of copper (II) - oxine chelate when shaken with the drug solution in buffer medium of pH 8. The drugs were determined in the concentrations 30-90 μg mL(-1) and 30-100 μg mL(-1) for captopril and penicillamine respectively, and the detection limits 0.94 and 1.76 μg mL(-1) for captopril and penicillamine respectively. The proposed methods were applied in the analysis of both compounds in their pharmaceutical preparations, and results were favorably compared with reference spectrophotometric methods regarding accuracy and precision.