Determinação condutométrica de captopril em formulações farmacêuticas utilizando sulfato de cobre(II) como titulante

A simple and rapid conductometric method for captopril determination using copper(II) sulphate solution as titrant was developed. The method was based on the chemical reaction between captopril and Cu(II) ions yielding a precipitate. The conductance of the solution was monitored as a function of the added volume of titrant. The method was applied with success for captopril determination in three pharmaceutical formulations. The relative standard deviation for six successive measurements was smaller than 0.5%. Recovery values from three samples, ranging from 97.7 to 103%, were obtained.

Co-eletrodeposição oscilatória de cobre e estanho

It is investigated in the present contribution the oscillatory co-electrodeposition of CuSn on a polycrystalline gold surface in the presence of Triton X-100 surfactant and citric acid as additive, in acidic media. The experiments were conducted under potentiostatic control and the system dynamics characterized in terms of the morphology and stability of the current oscillations. Besides modulations in the frequency and amplitude of the current oscillations, several patterned states were observed, including relaxation-like and mixed mode oscillations. The oscillations were found to be very robust and some time series presented regular motions up to about two hours.

Avaliação do efeito da concentração de carbonato na eletrodeposição de cobre sobre discos de aço-carbono

Mild steel blankets were covered with electrolytic copper thin layer, from cyanide bath, being evaluated the influence of the carbonate concentration in the physiochemical properties of those deposits. The cell voltage decreased as the current intensity decreased, but the adherence of the deposit was not enhanced, showing that the increment of carbonate concentration causes substantial problems. Chemical solubilization reactions of air-bearing carbon dioxide and oxidation of free cyanide ions through dissolved oxygen evolved in the anodic processes contribute to the copper plating to occur in an inefficient way. The best optimal conditions require a carbonate concentration below 50 g L-1.

Adsorção competitiva de inibidor de corrosão usado em poços de perfuração de petróleo sobre aço, esmectita e arenito

A commercial corrosion inhibitor used in petroleum production was characterized by means of infrared spectroscopy and energy dispersive spectroscopy (EDS). Predicting the adsorption behavior of corrosion inhibitor onto steel, sandstone and esmectite is the key to improve working conditions. In this study, the adsorption kinetics of inhibitor formulations in HCl 15% or in Mud Acid (HCl 13,5% and ammonium bifluoride) onto steel, sandstone and esmectite was determined by means of spectrophotometry. Kinetic parameters indicated that adsorption of inhibitor in the presence of bifluoride was favored. Moreover, the adsorption constant rate was the largest when the substrate was esmectite.

Estudo do comportamento eletroquímico de substâncias complexantes utilizando eletrodo de cobre

Copper electrode can be used for determination of complexing compounds through complexation reactions between Cu(II) and the analites. In this work some studies with three compounds were performed: glycine (precursor of glyphosate synthesis), herbicide glyphosate and aminomethylphosphonic acid (main metabolite of glyphosate). These compounds are complexing agents for Cu electrodes. Through simple experiments (cyclic voltammetry and corrosion studies) the applicability of the copper electrode as electrochemical sensor for complexing compounds in flow systems was presented.

Efeito de substâncias empregadas para remoção de cobre sobre o teor de compostos secundários da cachaça

High copper content is of great concern among producers of sugar-cane spirits who frequently use filters instead of cleaning the stills. This study compared the efficiency of activated carbon, ion-exchange-polymeric resin, and activated-carbon/iron-oxide magnetic composite for copper reduction without removing excessive organic compounds that are important for the beverage's quality. Resin was the most efficient copper adsorbent, removing fewer organic compounds. The composite also removed copper; however, it also removed large amounts of organic compounds. Activated carbon didn't remove sufficient copper to reduce its concentration to less than 5 g L-1, and it removed large amounts of higher alcohols and esters.

Corrosão metálica associada ao uso de combustíveis minerais e biocombustíveis

Fuels and biofuels have a major importance in the transportation sector of any country, contributing to their economic development. The utilization of these fuels implies their closer contact to metallic materials, which comprise vehicle, storage, and transportation systems. Thus, metallic corrosion could be related to fuels and biofuels utilization. Specially, the corrosion associated to gasoline, ethanol, diesel, biodiesel, and their mixtures is discussed in this article. Briefly, the ethanol is the most corrosive and gasoline the least. Few investigations about the effect of biodiesel indicate that the corrosion is associated to their unsaturation degree and the corrosion of diesel is related to its acidity.

Emprego de sílica gel organicamente modificada e impressa ionicamente para pré-concentração seletiva on-line de íons cobre

The present work purposes the preparation of a silica gel sorbent organically modified with 2-aminoethyl-3-aminobutylmethyldimethoxysilane (AAMDMS) and imprinted with Cu2+ ions by means surface imprinting technique and its use for selective on-line sorbent preconcentration of Cu2+ ions with further UV-VIS spectrophotometric determination by flow injection analysis. The Cu2+-imprinted silica gel, when compared with non imprinted silica gel and silica gel, showed from the binary mixture of Cu2+/Ni2+ relative selectivity coefficient (k') of 6.84 and 5.43 and 6.64 and 19.83 for the mixture Cu2+/Pb2+, thus demonstrating higher selectivity of Cu2+-imprinted silica gel towards Cu2+ ions. Under optimized condition, the on-line preconcentration method provided detection limit of 3.4 μg L-1 and linear range ranging from 30.0 up to 300.0 μg L-1 (r = 0.995). The accuracy of method was successfully assessed by analyzing different kind of spiked water samples with recovery values ranging from 92.2 up to 103.0%.

Evaluación de la toxicidad de cobre en suelos a través de biomarcadores de estrés oxidativo en eisenia foetida

Copper toxicity in soil was evaluated using biomarkers of oxidative stress (catalase enzyme activity, superoxide dismutase and lipid peroxidation) in the earthworm Eisenia foetida. Agricultural topsoils from mining areas of the Aconcagua river basin were collected. Total copper concentrations were in the range of 94-959 mg kg-1, while the exchangeable copper concentrations were in the range of 46-2225 µg kg-1. Earthworms exposed to soil with exchangeable copper concentrations above 32 µg kg-1 showed an increase in catalase activity. Parameters of antioxidant activity were more sensitive than the weight change and thus can be used as appropriate biomarkers in Eisenia foetida.

Avaliação da influência de sulfetos solúveis na complexação do cobre em águas superficiais empregando métodos voltamétricos

In this work a sulfide quantification protocol using voltammetric methods was developed to evaluate the effect of dissolved sulfides on copper complexation. On the basis of pH, sulfide release from the dissociation of specific metal sulfide complexes can be electrochemically measured and then removed (as H2S) by a N2 purge. Cathodic stripping square wave voltammetry (CSSWV) was conducted to quantify Cu sulfides complexes which dissociate at pH < 5.0 during the process of acid titration.

Determinação da densidade de corrente de corrosão em meios de baixa condutividade: uso de microeletrodos para minimizar a queda ôhmica

The gravimetric and electrochemical tests are the most common techniques used in determining the corrosion rate. However, the use of electrochemical polarization is limited to electrolytes with sufficient conductivity for which Tafel curves are linear. In this study, we investigated a technique in which working microelectrodes of AISI 1020 steel were used to obtain the Tafel curves in diesel oil. The strategy was to reduce the electrode area and hence the ohmic drop. The diameter of the microelectrode was reduced to a value where the compensation of the Tafel curves became unnecessary. The results showed that for electrodes with diameters below 50 μm, the ohmic drop tends to a minimum and independent of the microelectrode diameter.

Respuesta fisiológica de Euglena gracilis al estrés por cobre

The objective of this study was to evaluate the toxic effect of Cu2 + in the physiological development of E. gracilis. The results showed that E. gracilis had an effect on the dose-dependent growth to the concentration of metal. The exposure of E. gracilis metal at doses of 0.8 and 1.6 mM of Cu2+ showed a significant negative effect on the stability of DNA and photosynthetic pigments involved in capturing light in the antenna complex after 144 h of exposure to the metal.

Um método para avaliar a taxa de corrosão

In this paper it is proposed an indirect method to evaluate the corrosion rate of an aluminum and zinc alloy in alkaline solution by using a well-known device for collecting gases over water. The hydrogen gas formation, a corrosion product, is monitored at different time intervals and associated with the alloy mass loss. It has been suggested that the students should work in groups, which may make feasible the social interaction among them and that results discussion may be done collectively under a professor orientation. This proposal may propitiate the learning of terminology and involved concepts as well as contribute to a better understanding of corrosion phenomena that occur in their everyday life.

Avaliação do efeito de gases poluentes na corrosão metálica: um experimento para o ensino da corrosão

In this work one proposes a didactic experience to simulate atmospheric corrosion of copper and nickel, due to sulfur dioxide presence. This is an opportunity to understand some basic aspects of atmospheric corrosion, by using fundamental concepts in chemistry, reactions of extraction and characterization of pollutants, as well as their participation in corrosion process. This subject opens a space for discussion about necessity of pollutant gases emissions control for preservation of materials and the environment.

Avaliação da resistência à corrosão de implantes em aços inoxidáveis ISO 5832-9 e F138 removidos de pacientes

This work has compared the surfaces of two different steel samples used as orthopedical implants, classified as ASTM F138 and ISO5832-9, through optical emission spectroscopy, by means of SEM and EDS. The samples (implants) were also submitted to potentiodynamic cyclic polarization in Ringer lactate and NaCl 0.9 M L-1 solutions; ISO5832-9 sample did not show any kind of localized corrosion, but in the case of F138 steel was observed a pit localized corrosion in both solutions. In Ringer lactate solution it was observed a loss of about 63% for nickel and 26% for iron for F138 stell, compared to the initial composition.