Portugaliae
Electrochimica Acta

The aim of this study is to evaluate the potential of benzotriazole (BTAH) for replacement of sodium nitrite (NaNO2) in the zinc phosphate bath (PZn+NaNO2) used for carbon steel (SAE 1010). Surface characterization of phosphated and unphosphated samples was carried out by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Optical Microscopy and X-ray diffraction. The corrosion resistance of the samples was evaluated by electrochemical techniques such as Open Circuit Potential, Electrochemical Impedance Spectroscopy and Anodic Potentiodynamic Polarization Curves, in a 0.5 M NaCl electrolyte at room temperature. The experimental results showed that not only benzotriazol (PZn+BTAH) presented better corrosion properties than sodium nitrite, but also the amount of the deposited phosphate increased approximately six times comparatively to the bath with sodium nitrite. The results demonstrated that benzotriazole (BTAH) is a potential candidate for replacement of sodium nitrite (NaNO2) in zinc phosphate baths.

Quetiapine (QTF) is a potent serotonin and dopamine receptor antagonist used to treat major depressive disorders and schizophrenia. A simple, precise, accurate and cost-effective titrimetric method for the determination of QTF in bulk drug and in its dosage forms has been developed and validated. The method is based on the potentiometric titration of QTF in glacial acetic acid with acetous perchloric acid using a modified glass-saturated calomel electrode system. The method is applicable over the range of 2.0 – 20.0 mg of QTF. The proposed method was successfully applied to the determination of QTF in its pharmaceutical dosage forms. The results obtained were favorably compared with those obtained using a reference method. The precision results, expressed by intra-day and inter-day relative standard deviation values, were satisfactory (RSD ≤ 1.2%). The accuracy was satisfactory as well (RE ≤ 1.33%). Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedures, as shown by the recovery study via standard addition technique with percentage recoveries in the range 98.25-101.0 %, with a standard deviation of ≤ 0.62-1.52%.

The corrosion behaviour of Al 6061-TiO2 particulate composites in chloride, nitrate, sulphate and acidic media has been studied in the present investigation. The unreinforced matrix, and the composites containing 2, 4 and 6 weight percent of TiO2 particulates were prepared by liquid metallurgy route using the vortex technique. Their corrosion behaviour was evaluated by weight loss, potentiodynamic polarisation, scanning electron micrograpaph (SEM) and energy dispersive X-ray analysis (EDXA) methods. The studies show that corrosion current density (ICorr) and the corrosion rate were highest in the case of corrodent 0.1 N HCl. The rate of corrosion of both the matrix alloy and the composites decreased with increase in time of exposure in acid medium, possibly due to the formation of a passive oxide layer. Corrosion current (ICorr), corrosion potential (ECorr) and pitting potential (EPit) were obtained from potentiodynamic polarisation studies. In all the media, the ICorr values of unreinforced matrix alloy and composites were found to increase as the TiO2 content increased from 0% to 6%, which could be attributed to the microgalvanic coupling between the reinforcement or conducting interfacial products and the matrix alloy. Insulator TiO2 particulates are perceived to act as inert material and degrade the integrity of the protective oxide layer on the Al matrix alloy. The presence of reinforcement in the matrix increases cathode to anode ratio in the composites, resulting in the formation of pits during localised corrosion. Moreover, the pitting effect was more pronounced in the presence of aggressive Cl- ions compared to mild NO3- and SO42- ions. SEM and EDX analysis of samples in chloride media showed the presence of large pits and completely deteriorated surface, complementing weight loss and polarisation studies.

Three new gemini surfactants referred to as n-2-n (where n= 6, 12, 16) were developed as corrosion inhibitors for mild steel. Their critical micelle concentration (cmc) at equilibrium in water at 30oC was determined. Corrosion inhibition studies of mild steel in formic acid by gemini surfactants were conducted by using weight loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. Scanning electron microscopic study (SEM) was also used to investigate the surface morphology of inhibited and uninhibited metal samples. The results obtained show that the surfactants studied are good mixed type inhibitors. The result was also correlated with several factors, including the chain length of the hydrophobic chains, critical micelle concentration (cmc) and adsorption free energy of these inhibitors. The adsorption of all the gemini surfactants was found to follow Langmuir adsorption isotherm. EIS results indicate that the change in the impedance parameters (Rt and Cdl) with concentration of inhibitors was due to the formation of a protective layer on the surface of mild steel.

Poly(3,4-ethylene dioxythiophene) (PEDOT), poly(aniline) (PANI) and their copolymer (PEDOT-PANI) were electrodeposited onto a glassy carbon electrode. The electrodeposition was performed using cyclic voltammetry from acidic solution containing appropriate monomer concentrations and sodium dodecyl sulphate (SDS) as a wetting agent. The resulting polymer films were characterised using cyclic voltammetry in acidic and neutral phosphate buffer solutions and IR spectroscopy. The specific capacitance of the PEDOT-PANI co-polymer reaches up to 260 F g−1 and had good stability during cycling in mineral acid solution. IR spectroscopy confirms the formation of PEDOT-PANI copolymer. The polymers showed an electrochemical activity towards ascorbic acid oxidation. The oxidation current was linearly dependant up to 20 mM ascorbic acid concentration and the PEDOT activity was much higher than that for PANI and PEDOT-PANI copolymer.

A simple, accurate and sensitive voltammetric method for determination of donepezil (DNZ) using β-cyclodextrin modified carbon paste electrode (CDMCPE) is developed. CDMCPE exhibited significantly increased sensitivity and selectivity for DNZ compared to the bare carbon paste electrode (CPE). Effect of accumulation potential, accumulation time, pH of buffer, etc., on peak currents for the determination of DNZ was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Peak currents showed a linear response in the concentration range 4.2 x 10-8 to 5.6 x10-7 M and 3.2 x 10-9 to 4.2 x 10-8 M at CPE and CDMCPE respectively. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.2 x 10-9 and 0.40 x 10-8 M. The proposed method has been successfully applied for the determination of DNZ in spiked urine samples, serum samples and pharmaceutical formulations.