Nickel-dimethylglyoxime complex (abbreviated as Ni(II)(DMG) 2 ) modified carbon paste and graphite electrodes were prepared by mixing Ni(II)(DMG) 2 with graphite paste, and coating Ni(II)(DMG) 2 to the graphite surface. It is necessary to cycle the electrode potential to a high value (e.g. 0.8 V versus SCE) for the preparation of the modified electrodes. The electrochemical reaction was originally assumed to be a one-electron process converting Ni(II)(DMG) 2 toNi(III)ONi(III)(OH)(DMG) 2 ] -showed a strong catalytic activity toward electro-oxidation of methanol and ethanol. The electrocatalytic oxidation currents consistently increase with the increase in Ni(II)(DMG) 2 loading, OH -, and alcohol concentrations. Rotating disk electrode results obtained with a Ni(II)(DMG) 2 coated graphite disk electrode showed that the electrocatalytic oxidation of alcohol is a 4-electron process producing formate anion (methanol oxidation) or acetate anion (ethanol oxidation). A mechanism for the electrocatalytic oxidation of methanol/ethanol was proposed, and a rate-determining step was also discussed.

A ruthenium (III) hexacyanoferrate (Ru(HCF)) film coated on a glassy carbon electrode was explored as an electrocatalyst for hydrazine oxidation. Surface cyclic voltammograms of Ru(HCF) film showed four reversible one-electron redox waves. Two, which corresponded to the redox processes of Ru(III)/Ru(IV) and Fe(II)/Fe(III), were identified to be responsible for the catalytic activity of hydrazine oxidation. Kinetic studies using potential scan rate dependency, Tafel plots, and rotating disk electrode technique found that this catalyzed hydrazine oxidation was a complete four-electron/four-proton process producing N 2 , with the rate determining step possibly a one-electron process with a transfer coefficient (a) of *0.31-0.36. In addition, based on kinetic analysis and findings in the literature, we propose a possible reaction mechanism for catalyzed hydrazine oxidation in order to facilitate further understanding.

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A glassy carbon electrode modified with a ruthenium (III) hexacyanoferrate film was investigated for the determination of captopril in pharmaceutical formulations. The RuOHCF film was deposited on the surface of the electrode after applying 50 successive cycles and subsequent stabilization in a mixture of NaNO3 0.50 mol L−1+HCl 0.050 mol L−1 used as supporting electrolyte. The main processes responsible for the redox electrode response are attributed to the system RuII/RuIII/RuIV, and appeared at −0.080, 0.86 and 1.01 V (vs. SCE). The redox process at −0.080 V was selected for the determination of captopril in the present study, once it provided higher sensibility and occurs in a lower potential than the other ones which can prevent interferences. The experimental parameters used in the determination of the analyte, using differential pulse voltammetry were optimized: pulse amplitude: 50 mV, scan rate: 5 mV s−1 and potential window: −0.5 to 0.2 V (vs. SCE). The analytical application of the sensor in real samples demonstrated a linear range between 0.060 and 0.80 µmol L−1 (r=0.998) with a detection limit of 0.047 µmol L−1. A mechanism based on co‐precipitation of captopril and the Ru (III) complex in the film is presented once the signal of the RuII/III redox couple decreases with increasing the analyte concentration. Recoveries of 99 to 100 % were achieved in pharmaceutical samples and the proposed procedure agreed with the HPLC official method within 95 % confidence level, according to the t‐Student test.

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