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A composite electrode comprised of graphite, Nujol, and nanoparticles of Fe2O3 core–cobalt hexacyanoferrate shell was prepared and the charge transport processes in the bulk of this composite were studied. The electrode/solution interface was assumed as a binary electrolyte whose charge transport occurred between redox sites of the nanoparticles present in the composite and counter cations present in the solution. Using cyclic voltammetry, the diffusion of counter cation in the shell was investigated. Using chronoamperometry, an effective diffusion coefficient and its dependency on the applied potential was obtained. In the Nyquist diagrams, different time constants were appeared with relation to different physical and electrochemical processes. Percolation of electron in the shell of the nanoparticles appeared at very high frequencies and exhibited the feature of a diffusion process with a transmissive boundary condition at interface of core–shell structure/graphite particles. The diffusion coefficients of electron and counter cation and the standard rate constants of each individual electrochemical reaction were obtained.

Electrocatalytic oxidation of deferoxamine was studied on carbon paste electrodes modified with nanoparticles of iron(III) oxide core-cobalt hexacyanoferrate-shell using cyclic voltammetry and chronoamperometry. Voltammetric curves represented two quasi-reversible redox transitions which in the presence of deferoxamine, the two anodic peak currents increased, followed by decreases in the corresponding cathodic currents. This indicated that deferoxamine was oxidized on the immobilized cobalt hexacyanoferrate via two electrocatalytic steps. The rate constants, the electron transfer coefficients and the diffusion coefficient involved in the electrocatalytic oxidation of deferoxamine were reported. A sensitive and time-saving determination procedure was developed for the analysis of the drug in both batch and flow systems, and the corresponding analytical parameters were reported. The proposed amperometric method was also successfully applied to the direct assays of spiked human serum with iron–drug complex.

The electrooxidation of dextromethorphan on a composite constructed with carbon nanotube–ionic liquid–carbon microparticles was investigated by cyclic voltammetry in a 100 mM phosphate buffer solution, pH 7.40. In the voltammograms, an irreversible diffusion-controlled anodic peak appeared. The diffusion coefficient of dextromethorphan, the electron-transfer coefficient, and the standard rate constant of the electrooxidation process were found to be 3.45 × 10−6 cm2 s−1, 0.65, and 1.67 × 10−3 cm s−1, respectively. A sensitive and timesaving determination procedure was developed for the analysis of dextromethorphan, and the corresponding analytical parameters were reported. Using this method, dextromethorphan was determined with an LOD and LOQ of 8.81 and 29.36 μM in a linear range of 2.5 × 10−4 to 3.3 × 10−3 M, respectively. The proposed amperometric method was successfully applied to the analysis of commercial pharmaceutical products (syrup and oral drop), and the results were in good agreement with the declared values.

The electrooxidation of several non-steroidal anti-inflammatory drugs (indomethacin, mefenamic acid, and diclofenac) was investigated on nanoparticles of Ni–curcumin-complex-modified glassy carbon (n-GC) electrode in alkaline solution. Surfaces studies were performed by scanning electron micrographs and atomic force microscopy. The oxidation process and its kinetics were studied using cyclic voltammetry and chronoamperometry techniques and also pseudo-steady-state polarization measurements. Voltammetric studies indicated that, in the presence of drugs, the anodic peak current of low-valence nickel species increases, followed by a decrease in the corresponding cathodic current. This pattern indicates that drugs were oxidized on the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Ni(III)-active sites and their subsequent consumption by drugs was proposed. The rate constants of the catalytic oxidation of drugs and the electron-transfer coefficient are reported. A sensitive, simple, and time-saving amperometric procedure was developed for the analysis of these drugs in bulk form and for the direct assay of tablets, using the n-GC electrode.

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10−6 cm2 s−1. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10−6 M with the proposed method.

The electrocatalytic oxidation of aspirin has been investigated on a nickel oxide-modified nickel electrode in alkaline solution. The process of oxidation and its kinetics have been investigated by using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques and also steady-state polarization measurements. Voltammetric studies have indicated that in the presence of aspirin, the anodic peak current of low-valence nickel species increases, followed by a decrease in the corresponding cathodic current. This indicates that aspirin was oxidized on the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The rate constant of the catalytic oxidation of aspirin and the electron transfer coefficient have been found to be 1.15×105 cm3 mol−1s−1 and 0.49, respectively. Impedance measurements show that aspirin is diffused into the bulk of the modifier film, and the oxidation process of aspirin occurs in the bulk of nickel oxide film. It has been shown that by using this modified electrode, aspirin can be determined with a detection limit of 4.8×10−5 and successfully applied for determination of aspirin in tablet.