Portugaliae
Electrochimica Acta

The corrosion inhibition of aluminum, in 0.1 M Na2CO3, by Mentha pulegium essential oil, was studied using both polarization and impedance methods. The results show that Mentha pulegium is an effective inhibitor, providing an inhibition rate of 94.16 %, with a concentration of 800 ppm. The polarization study shows that the Mentha pulegium essential oil acted as a mixed inhibitor in 0.1 M Na2CO3. The activation energy calculation has proved that the inhibitor molecules adsorbed onto the aluminum surface, according to the physisorption mechanism.

Electrochemical oxidation of N-acetyl-p-aminophenol (AAP) and selected pharmaceutical products containing AAP is described in this study. Investigations were carried out at Pt electrode, with the application of cyclic (CV) and differential pulse (DPV) voltammetry. AAP was irreversibly oxidized in, at least, one electrode step, with potentials lower than the potential at which oxygen evolution started. Electrochemical methods based on voltammetric techniques (DPV and CV) have been developed for AAP determination in commercial pharmaceutical drugs. AAP content in pharmaceuticals was determined on the base of dependences of current intensity (electroanalytical measurements) and absorbance (UV-VIS spectra). The obtained results using both methods were in good agreement. The validation of CV, DPV and spectrophotometric methods is also presented. Spectrophotometric and voltammetric responses linearly increased with increasing AAP concentrations, in the range from 0.2 to 5 mmol L-1, with a correlation coefficient of 0.997 (UV-VIS), 0.999 (CV) and 0.998 (DPV). Both electrochemical methods are simple, reliable and sufficiently accurate and precise for AAP quantification in commercial drug samples (tablets). The analysis took only 5 minutes of manual operation, including Pt electrode pre-treatment.

The inhibitive action of Chromolaena odorata stems extract, in various concentrations, against mild steel corrosion in a 1 M NaCl solution, was studied using weight loss, potentiodynamic polarization methods and scanning electron microscopy. Maximum inhibition efficiency of 99.83 % was obtained, at 303 K, for an extract concentration of 3000 mgL-1. The activation and free energies for the inhibition reactions supported the physical adsorption mechanism. The extract adsorption onto the mild steel surface was found to be exothermic, spontaneous, and to obey the Langmuir adsorption model. FT-IR analysis showed the presence of hydroxyl (OH) and carbonyl(C=O) functional groups and aromatic rings in lignin, which are the binding groups that might be responsible for lignin’s inhibitive action against mild steel corrosion. Furthermore, SEM analysis revealed that the mild steel surface was affected by lignin’s adsorption, due to the formation of a protective film.

This paper has carried out the construction and evaluation of a selective electrode for silver, using 5-(4-dimethylaminobenzylidene)rhodanine as ionophore, and diocthyl phthalate (DOP) with plasticizer in PVC. The electrode shows fast potentiometric responses in the concentration range from 10-6 to 10-2 mol/dm3, with Nernstian slope (58.2 ± 0.8 mV/decade), and a response time of 20 s. Also, we presented a theoretical study of the molecule, optimized by DFT to a B3LYP/6-31G (d, p) level of theory. A good agreement was obtained between calculated geometrical parameters using DFT methods and experimental data. Analysis of the ionophore by the natural bond orbital (NBO) allowed explaining the possible centers of coordination with Ag+. Other characteristics of the electrodes were also studied.

The goal of this study was to propose an electrochemical sensor for Paracetamol determination. To reach this objective, a graphite electrode (GE) was modified with iron oxides, and it was tested in an alkaline aqueous solution, in order to appreciate its electrocatalytic properties towards paraacetylaminophenol anodic oxidation. The graphite electrode modification was performed, in a first step, by potentiostatic deposition of an iron film at -1 V/SCE, in an aqueous solution of 0.04 M Fe (NO3)3 + 0.15 M KNO3, followed, in a second step, by cyclic voltammetry in an aqueous solution of 0.1 M sodium hydroxide, at 25 ºC. The modified electrode was characterized by means of scanning electron microscope coupled to an EDAX X-Ray micro-analyser. Paraacetylaminophenol determination by means of this novel sensor was instantaneous in an alkaline solution. The performance of this sensor was obtained in the concentration range from 13 ppm to 320 ppm, with a sensitivity of 1.6×104 µA mol-1 L.