Determination of some antihypertensive active substances from pharmaceutical dosage forms and biological fluids using modified glassy carbon electrodes with electroanalytical methods

In this thesis study, modified glassy carbon electrodes were developed for the sensitive determination of the electrochemically active antihypertensive active substances doxazosin mesylate, amlodipine besylate and bisoprolol fumarate by voltammetric methods. The glassy carbon electrode surface was modified by coating multi-walled carbon nanotubes and/or naphthol green B dye in different combinations on the electrode surface. For each active substance, among the modified electrodes prepared in different combinations, the modification that gave the highest peak current and the most symmetrical peaks was selected and analysis studies were carried out with these electrodes. For the analysis of active substances, cyclic voltammetry, differential pulse voltammetry, and square wave voltammetry methods were used. Suitable buffer media for analysis were determined as pH 5.5 acetate buffer for doxazosin mesylate, pH 7.0 phosphate and pH 5.5 acetate buffers for amlodipine besylate, and pH 7.0 phosphate buffer for bisoprolol fumarate. Scan rate studies showed that doxazosin mesylate and amlodipine besylate had an adsorption-controlled process and bisoprolol fumarate had a diffusion-controlled process. Deposition potential, deposition time, and stirring rate were optimized for adsorption-controlled active substances. Calibration graphs were obtained using voltammetric methods for the quantitative analysis of each substance under specified conditions; linear working ranges, detection and quantification limits were determined. The precision of the developed methods was calculated based on five values through intra-day and inter-day repeatability experiments and was obtained below 2%. Finally, the active substances were determined from pharmaceutical dosage forms, human serum, and artificial urine samples using the developed methods. Accordingly, at least one method developed for each active substance could be applied to both pharmaceutical dosage forms and biological samples. This showed that active substances could be analyzed with high accuracy without the influence of other substances in the samples.