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.

Electrochemical study of hydrochlorothiazide and its determination in urine and tablets.

A voltammetric study of hydrochlorothiazide (HCTZ) at glassy carbon electrode was carried out. The drug in Britton-Robinson buffer (pH 3.3) is oxidized at +1040mV, giving rise to a well-defined peak. Cyclic voltammetric study indicates that the oxidation process is irreversible and diffusion-controlled. A sensitive, simple and time-saving differential pulse anodic voltammetric procedure has been developed. The procedure has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has been validated. The limit of detection for the standard solution was 5.0ngml(-1) and for the drug in urine was 14.0ngml(-1). The results obtained from the analysis of commercial tablets were compared statistically with those obtained from the USP 26 high-performance liquid chromatographic (HPLC) method.

Spectrophotometric determination of omeprazole, lansoprazole and pantoprazole in pharmaceutical formulations.

The compensation method and other chemometric methods (derivative, orthogonal function and difference spectrophotometry) have been applied to the direct determination of omeprazole, lansoprazole and pantoprazole in their pharmaceutical preparations. The methods have been validated; the limits of detection were found to be 3.3x10(-2), 3.0x10(-2) and 3.5x10(-2) microgram ml(-1) for the three drugs, respectively. The repeatabililty of the methods were found to be 0.3-0.5%. The linearity ranges were found to be 0.5-3.5 microgram ml(-1). The proposed methods have been applied to the determination of the three drugs in their grastro-resistant formulations. The difference spectrophotometric (DeltaA) method is unaffected by the presence of acid induced degradation products; hence can be used as a stability indicating assay.