Construção de uma cela de fluxo para medidas por espectrofotometria em fase sólida

A simple and low cost flow cell is proposed for measurements by solid-phase spectrophotometry employing a conventional spectrophotometer. The flow cell geometry allows the employment of a large amount of the solid support without causing both excessive attenuation of the radiation beam and increasing of the back-pressure. The adaptation of the flow cell in the optical path of the spectrophotometer in order to increase the precision is discussed. The flow cell characteristics were demonstrated by measurements of Co(II), employing 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C18 bonded silica as solid support. The apparent molar absorptivity and coefficient of variation were estimated as 1.86 x 10(5) L mol-1 cm-1 and 1.4 % (n=15). A sample throughput of 40 determinations per hour and a detection limit of 15 mug L-1 (99.7 % confidence level) were achieved.

Novas tendências para o tratamento de resíduos industriais contendo espécies organocloradas

The toxic character of organochloride compounds, their habitual presence in many industrial effluents, and mainly the low efficiency of the current remediation processes, are important aspects that have been promoted to study new degrading technologies. Among the great number of new physical and chemical alternatives, the photochemical and electrochemical processes have been played an important role, mainly due to their high degradation capacity through relatively low-cost procedures. In these contexts biological processes, the use of white-rot fungi, or even ligninolytic enzymes produced from them, are also very promising alternatives. However, the necessity of long reaction time and the high cost of the enzyme production process are some of the drawbacks that difficult the definitive consolidation of these processes.

Análise dos álcoois, ésteres e compostos carbonílicos em amostras de óleo fúsel

Analysis of alcohols, esters and carbonyl compounds were performed using HRGC and HPLC techniques in samples of fusel oils from three different Brazilian alcohol distilleries. High content of isoamyl alcohol (390 g.L-1), isobutyl alcohol (158 g.L-1), ethyl alcohol (28,4 g.L-1), methyl alcohol (16,6 g.L-1) and n-propyl alcohol (11,9 g.L-1) were found. These compounds represent 77 ± 8 % of the approximated weight of a liter of fusel oils. The obtained results show the feasibility of using fusel oils as low-cost raw material for the synthesis of chemicals.

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.

Computação em química teórica: informações técnicas

The purpose of this work is to demonstrate the usefulness of low cost high performance computers. It is presented technics and software packages used by computational chemists. Access to high-performance computing power remains crucial for many computational quantum chemistry. So, this work introduces the concept of PC cluster, an economical computing plataform.

Propulsor pneumático versátil e isento de pulsação para sistemas de análise em fluxo

Aquarium air pumps are proposed and evaluated as pneumatic liquid propulsion devices for flow injection and continuos flow analysis (FIA and CFA) systems. This kind of pump is widely available at a very low cost and it can sustain a pressure around of 4 psi (0.28 bar) indefinitely. By applying this air pressure onto a solution contained in a reservoir flask, it is possible to reach flow rates of up to 12.5 mL min-1 for circuits comprising reactors, made from 0.8 i.d. tubing with a length of 100 cm. The precise adjustment of flow rate below the maximum one can be made with a simplified needle valve or inserting in series a short length of capillary tube. The absence of flow pulsation is a definite advantage in comparison with peristaltic pumps, especially when amperometric detection is elected, as confirmed experimentally in FIA and CF applications.

Sacarose no laboratório de química orgânica de graduação

An experiment showing the readily available disaccharide (sucrose) as reagent for experiments in undergraduate chemistry laboratory is described. The preparation of 2,3:4,5-di-O-isopropylidene-beta-D-fructopyranose from sucrose is very simple, uses low cost materials, requires two periods of 4 hours and is useful for classroom support in undergraduate courses.

Nano vitrocerâmica de escória de aciaria

The manufacture of glass-ceramics is an alternative route for the commercial use of metallurgical slags. Such types of glass-ceramics may find commercial applications owing to their low cost, good mechanical properties and superior visual aspect. Besides, due to the elimination of that industrial residue from the environment and also due to the possibility of replacement of natural stones such as marbles and granites, the use of slags is an activity with strong ecological appeal. While the use of blast-furnace slags for the production of glass-ceramics is well known, the utilization of steel making slags constitutes a challenge, because these materials possess low concentration of SiO2. In this work a novel composition for producing glasses and glass-ceramics from a steelmaking slag is presented. The crystal nucleation kinetics, the characterization of the resulting microstructures for two different thermal treatments and mechanical properties of the glass-ceramics are discussed. A glass-ceramic having a marble aspect, fine volumetric crystallization, high degree of crystallization and improved mechanical strength was obtained.

A quimiluminescência como ferramenta analítica: do mecanismo a aplicações da reação do luminol em métodos cinéticos de análise

Relevant aspects of proposed mechanisms of the chemiluminescent reaction of luminol are presented and commented to emphasize its perspectives for kinetic analysis. A careful search for analytical applications of this reaction is discussed in order to point out new trends of the studies. Kinetic analysis using the luminol reaction is proposed to be a very attractive due to the good performance of the reaction in analytical applications and the positive characteristics of kinetic analysis, such as low cost and sensibility. It is pointed out that kinetic analysis using the chemiluminescent reaction of luminol should be encouraged.

Utilização de zeólita preparada a partir de cinza residuária de carvão como adsorvedor de metais em água

Coal ashes produced in coal-fired power plant could be converted into zeolites and can be used as low-cost adsorbents for the treatment of effluents contaminated with high levels of toxic metals. The capacity of synthetic zeolites for the removal of cadmium, zinc and copper ions from aqueous solutions has been investigated under different operating conditions. Zeolite from bottom chimney showed higher removal efficiency for metals ions than zeolite from feed hopper and mixing mill. The results indicated that the treated bottom ash could be applied in environmental technology as an immobilizer of pollutants.

Desenvolvimento de um dispositivo de baixo custo para medidas por quimiluminescência

A simple and low cost device (ca. US$ 150) that comprises two photodiodes fixed in lab-made Perspex flow cell is proposed for chemiluminescence measurements. The characteristics of the device (large observation window and reduced thickness) allow maximizing the amount of the emitted radiation detected. A sensitivity improvement of ca. 50 % was observed by employing two photodiodes for signal measurements. The performance of the device was assessed by the oxidation of luminol by hydrogen peroxide, yielding a linear response within the range of 2.50 to 500 µmol L-1 H2O2. The detection limit was estimated as 0.8 µmol L-1 hydrogen peroxide which is comparable with those obtained by using equipments based on photomultipliers.

Desenvolvimento de um dispositivo para obtenção de monocristais de ligas à base de cobre

This paper describes the drawing, construction and optimization of a device, which can be used to obtain single crystals of different metallic materials with melting point from 550 to 1050 ºC. Components of ease obtaining and of low cost were used. The device was based on the modified Bridgman technique and it was used to obtain single crystals of copper-based alloys. The temperature axial profiles and a difference less then 1% in the temperature between the wall and the center of the ceramic tube in the critical region for obtaining single crystals of good quality indicated that the oven presents a good thermal stability. Single crystals of CuZnAl and CuAlAg alloys of good quality were growth and characterized using optical microscopy and Laüe X-ray back reflection.

Desenvolvimento de um sistema automatizado para a fabricação de filmes automontados

In this technical note, we describe the construction of a low-cost computer controlled device for layer-by-layer film fabrication. The software allows to control multiple material deposition, washing and drying steps and the time for each operation. To test the device, we produced and characterized self-assembled films of conductive polymers by alternating poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA) via the layer-by-layer technique.

Estratégias para aumento de sensibilidade em espectrofotometria UV-VIS

Spectrophotometry is one of the most widespread analytical techniques due to its simplicity, reliability, and low-cost instrumentation for both direct measurements and coupled to other techniques or processes such as chromatography, electrophoresis and flow analysis. However, the application is often limited by sensitivity. This article describes some advances that greatly improve the performance of spectrophotometric measurements, especially in order to increase sensitivity, including the employment of liquid-core waveguides and solid-phase spectrophotometry.

Experimentos didáticos envolvendo radiação microondas

Theoretical and practical aspects of the use of microwave-assisted strategies in chemistry are introduced for students using simple and safe experiments employing a domestic oven. Three procedures are proposed for evaluating the distribution of microwave radiation inside the microwave oven cavity: (1) variation of the volume of marshmallows; (2) drying of filter paper wetted with Co(II) solution, and (3) variation of water temperature, after microwave-assisted heating. These experiments establish the position with the highest incidence of microwave radiation in the oven cavity, which was chosen for the synthesis of salicylic acid acetate. This synthesis was performed in 5 min of heating and the yield was around 85%. All experiments can be carried out in a 4 h lab-session using low-cost instrumentation.