Construção e aplicação de uma cela espectrofotométrica de camada delgada para análises em fluxo

A low cost spectrophotometric cell for use in flow analysis was manufactured in acrylic and adapted to a commercial spectrophotometer. The application of this cell was performed in the determination of chromium (VI) in steel samples using the reaction with the alkaloid brucine in presence of oxalic acid and 0.6 mol L-1 sulfuric acid. The cell allows an enlarged analytical range, diminishing the extension of dilutions, which is useful for on-line monitoring of industrial processes.

A utilização de materiais obtidos pelo processo de sol-gel na construção de biossensores

The use of sol-gel materials to develop new biosensors has received great attention due to its characteristics and versatility of sol-gel process. An overview is presented of the state-of-the-art of electrochemical biosensors employing sol-gel materials. Low-temperature, porous sol-gel ceramics represent a new class for the immobilization of biomolecules. The rational design of sol-gel sensing materials, based on the judicious choice of the starting alkoxide, encapsulated reagents, and preparation conditions, allows tailoring of material properties in a wide range, and offers great potential for the development of electrochemical biosensors.

Construção e aplicação de eletrodo de aço inoxidável UNS S31254 como eletrodo indicador em titulações condutimétricas

UNS S31254 SS electrodes have been built to substitute platinum in conductimetric titrations. The electrodes were tested in both acid-basic titration (chloridric acid and sodium hydroxide) and precipitation titration (sodium chloride and argentum nitrate as titrant). The practical application was exemplified from conductimetric tritations of HF ¾ HNO3 mixtures used in metalurgical industry to passivate stainless steels. The results were compared with those obtained using commercial platinum electrodes. The equivalent volumes obtained were comparable within 3% experimental error. Its application depends on the nature of electrolyte. These results have shown that stainless steel, less expensive than platinum (about three order of magnitude), can substitute platinum electrodes in routine analyses and didactic laboratories.

Aspectos técnicos envolvidos na construção de um "cluster beowulf"

Beowulf cluster is perhaps the cheapest way to construct a high performance computers. The strategy of reaching a high power computing isn't so difficult, but buying and configurating should be done carefully. Technical aspects of hardware components and message-passing libraries are considered, with some results given as examples.

Emprego de padrão único para a construção de curvas analíticas em sistema de análise por injeção em fluxo associado à espectrofotometria em fase sólida

In this work two procedures were proposed for analytical curves construction using a single standard solution employing a flow injection system with solid phase spectrophotometric detection (FI-SPS). A flow cell contends the chromogenic reagent 1-(2-tiazolylazo)-2-naphtol was positioned on the optical path. The first procedure was based on controlled concentration of analyte on solid phase and the relations between absorbance and the total volume of injected allowed the calculation of analyte concentration. The second procedure was developed employing controlled dispersion/retention in flow system where analyte concentration was obtained by exploiting the relation between transient signals of samples and single standard solution at equivalent reading time. The procedures were successfully applied for zinc determination in synthetic solutions with good precision and accuracy at 95% confidence level.

Construção de uma fonte de corrente e de uma sonda para medida de condutividade pelo método da sonda de quatro pontas

This paper describes the construction of an eletrical current source and of a probe to be used in the measurement of eletrical conductivity through a four-point probe method. These pieces of equipments can be obtained at the low price of US$ 50.00 and are adequate for eletrical conductivity measurements in the semiconductor range, that is from 10-1 to 10-6 S cm-1.

Preparação e caracterização do complexo cobaloxima e sua utilização na construção de um eletrodo modificado: um experimento eletroquímico no curso de graduação

The present experiment describes the preparation, characterization of n-butyl(pyridil)cobaloxime complex and its electrochemical property. The infrared and uv-visible absorption spectra were used to characterize the complex obtained. The infrared spectrum of the compound showed characteristics bands that indicated the formation of the Co-C chemical bond formation. The electronic absorption spectrum in acetonitrile showed transition bands attributed to p-p*, metal-to-ligand charge transfer, d-d transitions and charge transfer Co-C. The electrochemical property was investigated by the pulse differential voltammetry technique. Two oxidation processes: Co(I)/Co(II) at -423 mV and Co(II)/Co(III) at 752 mV were observed.

Um procedimento simples e barato para a construção de um equipamento "dip-coating" para deposição de filmes em laboratório

In this work we show how to build a piece of equipment for depositing thin films by the dip-coating process, using inexpensive components easily found on the market. This equipment allows us to control the dipping and pulling velocity at which the substrate is put in the film precursor solution, two very important parameters for obtain thin films. This article discusses the construction of the mechanical and electric parts of the equipment, a simple method to interface it to a computer and the development of the software to control the dip-coating parameters.

Construção e avaliação de célula de fluxo para estudo da tensão interfacial dinâmica da interface fluxo líquido - sólido por despolarização da fluorescência

A simple low-cost flow cell was developed, built and optimized in order to observe dynamic interfacial tension of continuous flow systems. Distinct materials can be used in one of the cell walls in order to observe the intermolecular forces between the flowing liquid and the chemical constitution of the walls. The fluorescence depolarization was evaluated using Rhodamine B as fluorescent probe seeded in ethylene glycol. The effects of the positioning angles on the data acquired across the cell are reported. The reproducibility of the data was evaluated with a spectrometer assembled in-house and the relative standard deviation was below 3%.

Construção e estudos de perfomance de um reator fotoquímico tipo CPC ("Compound Parabolic Concentrator")

A CPC (Compound Parabolic Concentrator) reactor was projected and constructed aiming to promote the degradation of the organic matter present in considerable volumes of aqueous effluents, under the action of solar radiation. The essays were done using a model effluent which consists of a mixture of fragments of a sodium salt of lignosulphonic acid possessing a mean molecular weigth of 52,000 Daltons, and a real effluent, from a chip board industry. The volume of effluent in each test was about 50 L. The tests involved heterogeneous (TiO2 P25 Degussa and formulations made from the association of TiO2 with a photosensitiser), and homogeneous (thermal and photochemical Fenton reactions) catalysis of the effluents. The results demonstrate the viability of application of this kind of reactor even when the load of organic pollutants is high.

Uso de membranas de Nafion para a construção de sensores ópticos para medidas de pH

The behaviour of Nafion® polymeric membranes containing acid-base dyes, bromothymol blue (BB) and methyl violet (MV), were studied aiming at constructing an optical sensor for pH measurement. BB revealed to be inadequate for developing sensing phases due to the electrostatic repulsion between negative groups of their molecules and the negative charge of the sulfonate group of the Nafion®, which causes leaching of the dye from the membrane. On the other hand, MV showed to be suitable due to the presence of positive groups in its structure. The membrane prepared from a methanolic solution whose Nafion®/dye molar ratio was 20 presented the best analytical properties, changing its color from green to violet in the pH range from 0.6 to 3.0. The membrane can be prepared with good reproducibility, presenting durability of ca. 6 months and response time of 22 s, making possible its use for pH determination in flow analysis systems.

Construção de campo de força empírico para estudo de complexos de Fe(III) com interesse bioinorgânico

In this work we present a new parametrization in molecular mechanics for studying iron complexes. This force field was implemented in the FORCES 2000 program, developed in our group for studying in coordination compounds of interest in bioinorganic chemistry. Mononuclear and dinuclear iron complexes were studied using this program with good success.

Construção de amostrador passivo de baixo custo para determinação de dióxido de nitrogênio

A new passive sampling system for monitoring NO2 in air has been developed to measure gas concentrations in indoor and outdoor air. The sampler is inexpensive, and easy to construct and operate. Nitrogen dioxide forms a derivative after reaction with a filter coated with triethanolamine and ethyleneglycol. The nitrogen dioxide derivative is extracted from the filter, and the concentration is determined by colorimetry. To test the sampler for measuring ambient level nitrogen dioxide, measurements were carried out inside homes and in a range of workplace environments.

Construção e aplicação de biossensores usando diferentes procedimentos de imobilização da peroxidase de vegetal em matriz de quitosana

Biosensors were developed by immobilization of gilo (Solanum gilo) enzymatic extract on chitosan biopolymers using three different procedures: glutaraldehyde, carbodiimide/glutaraldehyde and epichlorohydrin/glutaraldehyde. The best biosensor performance was obtained after the immobilization of peroxidase on chitosan with epichlorohydrin/glutaraldehyde. Linear analytical curves for hydroquinone concentrations from 2.5x10-4 to 4.5x10-3 mol L-1 with a detection limit of 2.0x10-6 mol L-1 and recovery of hydroquinone ranging from 95.1 to 105% were obtained. The relative standard deviation was < 1.0 % for a solution of 3.0x10-4 mol L-1 hydroquinone and 2.0x10-3 mol L-1 hydrogen peroxide in 0.1 mol L-1 phosphate buffer solution at pH 7.0 (n=8). The lifetime of this biosensor was 6 months (at least 300 determinations).

De resíduo a insumo: a construção do caminho para uma química mais limpa através de um projeto de ensino

The discussion among teachers, students, and technicians about the destination of residues from chemistry laboratories led to a research project whose results were incorporated into a course in its daily practices. The treatment of the residues from argentimetric practices allowed us to establish cognitive relations of technological basis and of those related to the rising of the level of awareness about environmental aspects and social responsibility of chemistry professionals. The techniques and the results, from the economic point of view, namely that of value aggregation (metallic silver) and the conversion of the residue into input (potassium chromate solution) are shown.