Francisco Claudece Pereira

Nanoelectrode ensembles for the direct voltammetric determination of trace iodide in water

Procedures for the preparation and characterisation of ensembles of gold nanodisk electrodes (NEE) of 30 nm diameter are presented, in particular focusing on improvements in the signal/background current ratios and detection limits with respect to the electrochemical oxidation of iodide and its analytical determination in water samples. At NEEs iodide undergoes a quasi-reversible diffusion controlled oxidation with a slight shift in E 1/2 values and slightly higher peak to peak separation with respect to conventional gold disk electrodes. The double layer charging current at the NEE is significantly lower than at conventional electrodes so that the detection limit (DL) by cyclic voltammetry with NEEs in tap water is significantly lower than DL at the Au-disk millimetre-sized electrode (DL 0.3 µM at NEE vs. 4 µM for Au-disk). Finally, it is shown that NEEs in combination with square wave voltammetry can be applied for the direct determination of iodide in water samples from the lagoon of Venice, with a detection limit of 0.10 µM.

Aplicações de nanoeletrodos como sensores na Química Analítica

Nanomaterials make up an emerging area in Chemistry and in the science of materials. This area constitutes the development of methods for synthesizing nanoscopic particles of a given material used for scientific investigation. Nanomaterials have a wide range of commercial possibilities and technological applications, including their use in analytical chemistry, as well as in electronics, optics, engineering, medicine, devices for liberation of drugs, bioencapsulation, among others. This paper presents a summary about nanoelectrodes, devices built from nanoparticles, which show great potential as electrochemical tools in many different types of analysis. The purpose of this paper is to review the construction methodologies of nanoelectrodes, and to point out their successful applicability in the various fields of immune assays and other analytical procedures with quantitative purposes.

Características ópticas e morfológicas de nanoestruturas de ouro

The present study describes a new procedure to obtain gold nanoparticles, directly in the pores of polycarbonate membranes commonly used in ultrafiltration. The dimensions of the particles may be controlled through the reduction time of the ions in the channels of the harbor matrix. The dissolution of the metallized polymer enables an investigation of the optical and morphologic properties of these elements.

DETERMINAÇÃO COLORIMÉTRICA DEMETABISSULFITO

Metabisulfite anion is widely used as an antioxidant agent and preservative of a number of industrialized products. The interaction of this agent with pararosaniline dye can reduce the absorption band of the pigment within the visible area. From the best experimental conditions such as Britton-Robinson buffer solution, pH 5.0, and dye in a solution of 1.0x10-4 mol L-1, it was possible to obtain a relation between concentration of metabisulfite and absorbance in a range from 1,3x10-6 mol L-1 to 3.0x10-5 mol L-1. The detection limit was calculated in 5.0x10-7 mol L-1. The methodology was applied on real samples.

Avaliação espectrofotométrica das formas CR+3, CRO4-2 e CR2O7-2

A spectrophometric study of the speciation of the chemical forms Cr+3, CrO4-2 and Cr2O7-2 was carried out on a wide interval of pH (from 2,0 to 12,0) in a Britton-Robinson buffer solution. The absorption spectra of the ultraviolet and visible regions are well defined and show bands in the two spectral regions. The relation between absorbance versus concentration for each chemical species allowed us to know the molar absorption coefficients of the chemical entities.

From Plates to Spheres: Tuning the Vanadyl Phosphate Morphology by Intercalation of Nitrosyl Oxide

The lamellar matrix VOPO4.2H2O was used to the intercalation of nitrosyl (NO) ligand. The vanadyl phosphate matrix, as well as the prepared intercalated compound (VOPO4.NO.H2O), were characterized by infrared spectroscopy, thermogravimetry, X-ray difractometry, and SEM microscopy. The X-ray diffraction patterns shown that the VOPO4.NO.H2O synthesis occurs with a decrease in the lamellar distance in comparison with VOPO4.2H2O. The SEM micrographs obtained for VOPO4.2H2O and VOPO4.NO.H2O shown that microstructure of vanadyl phosphate is flat square whereas the compound VOPO4.NO.H2O exhibits spheroid grains.

Monitoramento do corante pararosanilina em amostras biológicas

Pararosaniline dye (P) is a pigment which has a significant role in analysis of chemical substances and gram-positive and negative bacteria, as well as other microorganisms. Potentiometric essays of P have shown that the colorant is a weak monoprotic acid (pKa= 8,78); and the spectrophotometry allows to estimate its molar absorption coefficient as 1,48x104 mol-1 cm-1 L. The analytical curve for a determination of P has linearity between 7,36x10-6 and 7,36x10-5 mol L-1, and the methodology was application in biological samples.