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Quinine, a natural product, was investigated as a corrosion inhibitor for low carbon steel in 1.0 M HCl solution. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study the inhibition action in the temperature range 20-50°C. The corrosion of steel was controlled by a charge transfer process at the prevailing conditions. The electrochemical results showed that quinine is an efficient inhibitor for low carbon steel and an efficiency up to 96% was obtained at 20°C. The inhibition efficiency increases with inhibitor concentration and reaches a near constant value in the concentration range 0.48 mM and above. Application of the Langmuir adsorption isotherm enabled a study of the extent and the mode of adsorption.

A rapid and highly selective potentiometric method for the simultaneous analysis of peracetic acid (PAA) and hydrogen peroxide (H2O2) has been proposed, for the first time, using glassy carbon (GC) as an indicator electrode and I2/I- potential buffer. On the basis of the large difference in the reaction rates of PAA and H2O2 with I-, which was confirmed using stopped-flow spectrophotometry, a transient potential response corresponding to the reactions of the two species with I- was observed. The response times were typically a few seconds and several minutes for PAA and H2O2, respectively. The effects of the concentrations of molybdate catalyst, H+, I2, and I- in the potential buffer on the selectivity as well as the sensitivity were examined. The potential response obtained using the GC indicator electrode was found to be Nernstian over a wide range of their concentrations (typically from micromolar to millimolar) with slopes of 30.5 and 29.5 mV for PAA and H2O2, respectively (in close agreement with the theoretical value, that is, 29.6 mV). O2 was found to have no substantial effect on the potential change at the GC electrode in the present potential buffer.

The electrochemical behavior of peroxyacetic acid (PAA) in the presence of hydrogen peroxide (H2O2) has been investigated using cyclic voltammetry and hydrodynamic techniques [rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry]. The results have been analyzed aiming at simultaneous electroanalysis of both species. Glassy carbon and gold electrodes were used for this investigation. It was found that the reduction of PAA, as well as H2O2, is highly sensitive to the electrode material; for example, at 100 mV s-1, the reduction peak potentials of PAA were 0.2 and -1.1 V at gold and glassy carbon electrodes, respectively. The well-separated steady-state limiting currents were obtained using a gold electrode for the reduction of both PAA and H2O2 and also a well-defined one for the oxidation of H2O2. On the basis of the RDE experiments, good calibration curves were obtained for both species over a wide range of their concentrations, for PAA and H2O2 in the range of 0.36 to 110 and 0.11 to 34 mM, respectively. The simultaneous and selective electroanalysis of PAA and H2O2 in their coexistence is demonstrated for the first time.

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