Search

Hydrogen peroxide (H2O2) plays an important role as an intermediary in different biological, chemical and environmental systems. It has been widely used as an oxidizing and antimicrobial agent, in germicides production and textile and paper bleaching. However, it is well known, that H2O2 is a possible responsible in many diseases and is a chemical agent that threatens the environment, so it becomes important to detect peroxide with high accuracy. In this study, carbon paste electrode (CPE), modified with Co2SnO4 was synthesized and tested. It was successfully obtained a non-enzymatic H2O2 detection type sensor, based on Co2SnO4/ CPE composite, showing good linear response in concentration of H2O2 in the range of 88 - 605.9 μM.

This research demonstrates how the sulfite content can be measured by cyclic voltammetry using a previously reported membrane absorber system, which separates efficiently sulfite present in wine. Results obtained show notably similar values to those obtained for the same wine samples using modified Monier- Williams method (aspiration method) and Ripper method. The membrane absorber system allows the release of the free SO2, and can be used to determine the sulfur dioxide present in juices and other foods that contain high concentrations of phenols, polyphenols and other structurally related compounds that act as interferers in the electrochemical oxidation of sulfite. The absorber solution allows a direct measurement without change in pH or added electrolyte, facilitating the determination of great amounts of samples from diverse wines using only one calibration curve. In this way, a system that allows the detection of sulfite and that can be used in vineyards is obtained. Finally, the method was assessed on linearity, sensitivity, accuracy, reproducibility and repeatability, obtaining values that account for the applicability of the method.

The aim of this work is to study the sulfite oxidation mediated by glassy carbon electrodes modified with copolymers formed by ortho-phenylenediamine (OPD) and Co(II)-tetrakis(para-aminophenyl)porphyrin (CoTAPP). The copolymer was obtained through continuous cycling of potential of a glassy carbon electrode in acid medium containing each respective homopolymer in 1:1 feeding volume, in which the ortho-phenylenediamine concentration was 1·10-1 M and the CoTAPP concentration was 1·10-4 M. The film obtained is thin, stable and contains a low amount of porphyrin in comparison to the amount in orthophenylenediamine. Its electrocatalytic activity was tested toward the sulfite oxidation. In this case, this film is more electrocatalytic than the modified electrode modified with the CoTAPP electropolymer, even though ortho-phenylenediamine is inactive in this reaction. In this work the electrocatalysis process, the morphology of the film, and the difference of electrocatalytic behavior between the ortho-phenylenediamine and cobalt porphyrin homopolymers and the orthophenylenediamine-porphyrin copolymer were studied. The morphologic studies were done using Au electrodes since the electrocatalytic activity on Au and on glassy carbon are quite similar.

The success of Chilean wine in the international market has led to an important attention on the development of science and technology for wine differentiation, productivity, and quality. In order to report the profile of phenolic acid compounds in Chilean red wines, an SPE technique over ODS column was used followed by a reverse phase HPLC program that was developed to separate, characterize and quantify six phenolic acids (caffeic, gallic, p-coumaric, protocatechuic, syringic and vanillic acids) in four red Chilean wines varieties (Cabernet Sauvignon, Carmenere, Merlot and Syrah) from grapes cultivated in the central zone of Chile. The separation was carried out on an RP C-18 column using a binary gradient elution and diode array detection.

In this study, we compared four glassy carbon electrodes modified with adsorbed porphyrins of cobalt containing one, two, three, or four bis(methoxyphenyl) groups as substituents of the ligand. The aim of this work was to determine the effect of these donating groups on the electrocatalyst behavior of the modified electrodes for the reduction or oxidation of sulfite in water or in mixtures of 12% ethanol in water (v/v) at different pHs. The results showed that the modified electrodes are not catalytic toward the electro-reduction of sulfite in the whole range of pH studied (2-12). However, all the electrodes showed a catalytic toward the oxidation of sulfite at basic pHs. We found that the best catalytic system was the four-substituted porphyrin modified electrode at pH 9.8. This system performed well as an amperometric sensor for sulfite in ethanol-water mixtures and in aqueous solutions at the same pH. When the calibration curve was carried out by cyclic voltammetry, a detection limit of 0.10 mg L-1 for the four-substituted cobalt porphyrin modified electrode in water and in ethanol-water mixtures was found.

Low molecular weight carbohydrates (LMW) were determined in a Chilean Cabernet Sauvignon red wine by the Dubois method, a specific method for the determination of carbohydrates. Dialysis treatment of red wine allowed the separation of pentoses, hexoses, reducing and non-reducing oligosaccharides and glycosides (LMW) from the polysaccharides fraction (HMW) fraction. The total sugar content of red wine by Dubois method was 5.55 g/L. The content of LMW sugars determined by Dubois method (3.63 g/L) is higher than the sugar content of the polysaccharides fraction (1.78 g/L). Analysis of twenty more samples of Cabernet Sauvignon red wines showed that the high molecular weight fraction content is quite iterative (mean value 2.50 g/L). The advantage of the Dubois method in relation to Fehling method is that the former does not need prior decolouration of the sample and there is not interference of aldehydes. The method developed in this work may be a complementary method for the determination of carbohydrates in wine industry.

The aim of this work was the study of three different modified electrodes where the substrate and the porphyrin used to modify the electrodic surface was the same. The surface electrode was a glass covered by a layer of SnO2 doped with fluor. On this layer was formed a cubic spinel of Co-cobaltite. On this modified electrode was deposited or polymerized para-tetraaminophenylporphyrin of Ni (II). In each case, the treatment of the deposition of the porphyrin was different and the electrocatalytic behavior of the modified electrodes toward the oxidation of hydrazine drastically changes. In the case of a simple physically adsorbed layer of porphyrin, practically no electrocatalytic activity was found. In the case of a porphyrin deposited by reflux and cycled in basic solution, there is an important electrocatalytic activity giving N2 as product. This electrode was proved as an amperometric sensor of hydrazine and a very good linear relationship between current and concentration was determinate. Also, the polymeric electrode showed an important catalytic behavior toward the oxidation of hydrazine

Porphyrins and phthalocyanines of transition metals are good catalysts for many redox reactions [1-7]. In order to increase their catalytic activity it is often necessary to modify the macrocycle with donor or acceptor substituents making the species more reductive or oxidant depending on the analyte. However, this process is a one-way modification, because the molecule enhances or diminishes the electronic density of the metal by the substituent effect

Three monomeric iron and non-metalled tetraaminophenylporphyrins, with amino groups located in defferent positions of the phenyl substituents, were electropolymerized. These processes were carried out through continuous cycling of the potential on glassy carbon electrode surfaces. The aim of the work was to determine the effect of the amino groups’ position on the properties of the modified-electrodes. Phenyl substituents of the porphyrins were not conjugated with the macrocycle. Therefore, their substituents were only expected to modify the electropolymerization and not the potential of the redox metallic couples on the polymer. However, it was found that, when the complex is polymerized, the position of the amino groups greatly changes the potential of the iron couples. Thus, the electrocatalytic activity of the polymer-modified electrode toward the reduction of oxygen strongly depends on the position of amino substituents

The macrocyclic ligand, tetraaminophthalocyanine, was electropolymerized on a glassy carbon electrode by continuously potentiodynamic scans, using two different solvents, dimethylsulfoxide and dimethylformamide. In the first case, an over-oxidation can takes place, which partially destroy the film and inhibits its electrocatalytic activity for the reduction of oxygen compared to the polymer grown in dimethylformamide. To avoid this over-oxidation, two possible ways can be used: to achieve the electropolymerization during a lower number of potentiodynamic scans or using a positive potential limit shifted to more negative potentials. If a narrow potential interval is used, the electrocatalytic behavior of the polymer is similar to that obtained in dimethylformamide. However, if a wide potential interval is used but only during few potentiodynamic scans, it is possible to obtain a polymer with a new redox signal that presents a very interesting electrocatalytic activity for the reduction of molecular oxygen En este trabajo se realizó la electropolimerización por barrido continuo de potencial, de tetraaminoftalocianina sobre electrodos de carbón vítreo. Para esto, se utilizaron dos solventes, dimetilformamida y dimetilsulfóxido. En el caso del dimetilsulfóxido, se observa que a medida que transcurre la electropolimerización, empieza a ocurrir un proceso de sobre-oxidación que finalmente destruye al polímero, modificando e inhibiendo sus propiedades electrocatalíticas en la reducción de oxígeno, comparado con el polímero preparado en dimetilformamida. Para evitar esta sobre-oxidación, pueden utilizarse dos caminos: acortar el límite positivo de barrido de potencial, o bien, realizar la electropolimerización con un menor número de ciclos. En el primer caso, se logra evitar la destrucción parcial del polímero obteniéndose un electrodo de características electrocatalíticas similares al crecido en dimetilformamida. En el segundo caso, se obtiene un polímero que presenta una nueva señal redox y que es el de mayor electroactividad hacia la reducción de oxígeno