Camila Canales

Hydrazine electrooxidation mediated by transition metal octaethylporphyrin-modified electrodes

This work presents the generation of new systems composed of glassy carbon electrodes (GC) modified with commercially available transition metal octaethylporphyrins, M-OEP (M = CoII, CuII, ZnII, RuII, FeIII, NiII) for the electrooxidation of hydrazine at neutral pH. It was found that the most active system corresponds to GC electrodes modified with CoII-OEP adsorbed on the surface, evidencing the importance of the central metal. This system, whose preparation is quick and easy, has been reported to have great electrocatalytic activity on systems and unmodified GC electrodes, which has been corroborated by using electrochemical impedance spectroscopy techniques. In addition, this system provides a very good linear response to the analyte concentration, as well as high accuracy and exactitude. Thus, limits of detection and quantification of 0.0518 and 0.173 mmol L−1, respectively, were determined. These good characteristics envisage the possibility of developing a sensitive amperometric sensor. Furthermore, SEM, AFM and Raman studies revealed the actual modification produced on the electrode surface.

Electrochemical evaluation of ciprofloxacin adsorption on soil organic matter

Over the last decade, at both a national and international level, the amount and fate of pharmaceutical residues in the environment have become of public interest. Among the several types of pharmaceutical wastes, a particular fluoroquinolone called ciprofloxacin (Cipro) is worth mentioning. On the other hand, soil organic matter (OM) has proven to be capable of generating interactions with antibiotics, which results in a decrease in their availability. Therefore, the main goal of the current work is to investigate the adsorption of Cipro on humic acids (HA), and to evaluate an electrochemical adsorption experimental design to handle the HA special particle size and solubility. S-type adsorption isotherms are observed for Cipro adsorption on HA extracted from two volcanic soils, wherein a cooperative adsorption phenomenon exists. The Langmuir–Freundlich model was utilised to obtain the best fit. This model is especially effective at fitting HA–Andisol adsorption, R2 > 0.99. Adsorption on both HA presents n > 1, strongly suggesting the existence of cooperative adsorption. This comes from the macromolecular nature of the multiple functional groups, which results in multiple interactions. The analytical results of the electrochemical methodology are statistically precise and accurate. The electrochemical technique requires shorter adsorbent–adsorbate equilibration times than traditional methods and physical separation is not needed. A detailed particle size analysis shows that the adsorption is the most significant process in OM–ciprofloxacin interaction. In relation to analytical parameters of pharmaceutical samples (ciprofloxacin), a relative standard deviation of 1.85%, a percentage error of 1.53% and a 98.5% of recovery were obtained.

INCLUSION OF GLUTATHIONE PEROXIDASE ON POLYPYRROLE MODIFIED ELECTRODE, TO BE ASSAYED AS GLUTATHIONE SENSOR

In this work it was obtained a modified electrode by inclusion of the enzyme glutathione peroxidase (GPx) on a conductive polymer, polypyrrole (PPy), deposited on a graphite electrode (GC|PPy,GPx) for the amperometric detection of reduced glutathione (GSH) in presence of hydrogen peroxide. Also, working conditions were optimized in order to prepare the electrode GC|PPy,GPx, which were tested for different concentrations of monomer and enzyme, electrochemical type of perturbance (by fixed potential or cyclic voltammetry) deposition potential and time (PPy film thickness, GPx), etc. by testing the response of the electrodes versus GSH in presence of hydrogen peroxide at physiological pH and temperature. At optimal experimental conditions, the achieved electrode gives a characteristic response for the analyte, which means that this modified electrode can be proposed as a selective GSH sensor, since it was shown that the enzyme maintains its activity during experimental manipulations and responds in a highly reproducible mode, so its use is proposed as an amperometric biosensor which is highly selective and stable.

ELECTRODES MODIFIED BY Π STACKING OF METALLIC PHTHALOCYANINES AND ITS ELECTROCATALYTIC ACTIVITY ON NITRITE OXIDATION

ABSTRACT In this work, it proposed the developing of a new material, a modified electrode with metallic phthalocyanines stacking columns, MxPc (Mx = Co, Fe and Ni), assembled by p interactions, which have a behavior as a supramolecular system. These electrodes showed an important electrocatalytic activity against nitrite oxidation, compared to the same complexes monomer multilayers adsorbed on the electrode (M-MxPc). It is proposed two new obtaining methods of these systems, S1-MxPc, where the complexes would form a column and would be coordinated with the surface electrode through a covalent bond of 4-aminopyridine (4-AP), and S2-MxPc, where the own functional groups of glassy carbon (GC) would be the covalent unions able to coordinate the complexes and the columns formation. These covalent unions between the electrode surface and phthalocyanines, would give a directional stacking, and therefore, would modify both its electrocatalytical activity and its electrical features. It was also studied the dependence between the activity and the complex central metal (Co, Fe and Ni), finding a great dependence between them. It was found that the S2-MxPc modified electrodes were more stables and actives. The higher activity was found on S2-CoPc, which also performs a linear response. This last feature it is seen on a calibration curve with a large range of concentrations. It is important to notice that there is actually no relative information about the behavior of the new electrodes proposed on this work.

CHEMICAL FRACTIONS OF Al IN VOLCANIC SOIL AMENDED WITH CELLULOSE WASTE

The cellulose industry generates a great volume of organic and inorganic waste, one of these wastes are called dreg (D) and grits (G). These residues have a high content of calcium carbonate, positioning them as potential bleachers in acid soils. Due to the important content of Al in the residues, a sequential extraction was done to establish the metal chemical fractions such as exchangeable, adsorbed, organic carbonated, and the ones associated to sulfurs, in incubated samples (2, 4, 8, and 32 days at 60oC) of an Andisol amended soil with Grits, Dregs + Grits and lime in 1, 2 and 3 ton/ha doses. The results revealed that there was a significant increase in the amount of Al in all fractions, in comparison to the control soil. On the other hand the incorporation of these residues through a Dregs (70%) + Grits (30%) mixture provoked a pH increase, always higher than the commercial lime. Finally, the Al present on amended soils was mostly distributed in the residual and carbonated chemical fractions, which would constitute less labile chemical forms to the soil-solution.