Glutathione (γ-glutamylcysteinylglycine) is atripeptidethiol present in all eukaryotic and probiotic cells.¹ GSH is widely distributed biological cells and is involved in many important physiological phenomena including, protecting cells against oxidative damage influencing enzyme activity, and the synthesis of proteins and in the defense mechanism against abiotic stress.

Captopril (CAP), (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl] pyrrolidine-2-carboxylic acid, an active inhibitor of the angiotensin-converting enzyme (ACE) has been used for the treatment of hypertensive diseases and moderate heart failure as such or in combination with other drugs.

Vinylferrocene modified carbon nanotubes paste electrode (VFMCNTPE) was prepared and used as a sensitive and selective electrochemical method was developed for determination of Glutathione (GSH) and Captopril. Cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used as diagnostic and measurement techniques. Cyclic voltammetric investigation showed that GSH and Captopril didn’t show any distinguishable anodic peak in the scaning region potential 0 – 1.0V, versus Ag/AgCl electrode.Some of parameter such as pH for the determination of GSH & Captopril were optimized. pH=8 and 1% concentration Vinylferrocene percent for both of them were selected.

Typical SEM images of different electrodes showed After multiwall carbon nanotubes (MWCNTs) added to the carbon paste, it can be seen that MWCNTs were distributed on the electrode with special three-dimensional structure, indicating that the MWCNTs were successfully modified on VFMCNTPE. In addition, it can be clearly seen that the mediator dispersed homogeneously in modified electrode.

Under the optimized conditions, the electrocatalytic oxidation peak current of GSH showed two linear dynamic ranges with a detection limit of 0.09 μmol L^-1 GSH. The linear calibration ranges were obtained between 0.2-4.0 µmol L^-1 and 4.0-250.0 µmol L^-1 GSH using square wave voltammetry (SWV). The relative standard deviation (RSD%) for 5 replicated analysis of 10µM is 1.1%. The chronoamperometry was used to determine the catalytic rate constant and diffusion coefficient for the catalytic reaction of vinylferrocene with GSH. Interference study indicated that there is no interference except ascorbic acid.  Finally, the proposed sensor was also examined as a selective, simple and precise electrochemical sensor for the determination of GSH in real samples such as urine and hemolysed erythrocyte.

On the second work, the calibration curve for Captopril was linear in the concentration range from 0.2 to 400 µM and detection limit of 0.08 µM under the best experimental conditions selected.The relative standard deviation (RSD%) for 6 replicated analysis of 100 µM and 300 µM are 1.9%  & 2.1%, respectively electrochemical impedance spectroscopy was used to study the charge transfer properties at the electrode–solution interface. Also, the values of the catalytic rate constant (k), and diffusion coefficient (D) for Captopril were calculated. Although ascorbic acid shows interference, its interference can be minimized, if necessary, by using the ascorbic oxidase enzyme. Finally, the sensor was examined as a selective, simple, and precise new electrochemical sensor for the determination of captopril in real samples, such as drug and urine, with satisfactory results.

Keywords: Voltammetry; Multiwall carbon nanotubes paste electrode; Vinylferrocene; Electrochemical Impedance Spectroscopy; Glutathione determination; Captopril determination.