A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4x10(-7) to 4.1x10(-5)molL(-1) for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2x10(-8) and 9.3x10(-8)molL(-1), respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.
The present work evaluate the chemical conditions of the Murucupi river with relationship to the physical-chemical parameters and the presence of chemical elements in the water and correlations. The Murucupi river is located in the amazon region close the aluminum production area. Were analyzed the major, minor and trace elements (Ca, Mg, Na, K, Fe, Al, Ba, Mn, Sr, Zn, Ni, Pb e Cu), and physical-chemical parameters, acidity, total alkalinity, organic matter, pH, turbidity, temperature, conductivity, dissolved oxygen (OD) and total hardness. 13 collection points were selected along this river. In relation to the physical-chemical parameters the pH and OD only presented values in non conformity with the strip of values established by the resolution 357/05 of CONAMA. In relation to the chemical elements were found only the aluminum (Al: 356.04µg/L) and the iron (Fe: 1080.80µg/L), were in non conformity with the legislation. This results shows the anthropogenic influence in the contamination of the Amazon rivers from the production of aluminum reject.
___________________________________________________________________________________A água é uma das substancias mais importantes do planeta. É composta por hidrogênio e oxigênio, ambos de grande importância química e para vida humana. Embora na literatura científica existam vários estudos sobre as propriedades físicas e químicas da água, muito ainda pode ser estudado sobre essa substância. Neste estudo, descreveremos as propriedades elétrica e dielétrica da água na fase líquida, assim como, a impedância, constante dielétrica, polarização molar e momento dipolo em função da frequência (1-20 kHz) na faixa de temperatura entre 288 e 314 K. As medidas de constante dielétrica e impedância foram realizadas com auxílio de um analisador de impedância. Ademais, foi utilizado um sistema capacitivo de placas paralelas, todo experimento foi blindado para minimizar os efeitos de interferência eletromagnética (ruído) e conectado ao aterramento da rede elétrica do laboratório. Os valores de momento de dipolo foram estimados aplicando a teoria de Kirkwood com base na definição de campo local de Onsager para líquidos polares. Palavras-chave:Propriedades elétrica e dielétrica, Polarização molar e momento de dipolo, Teoria de Kirkwood.Water is one of the most important substances on planet. It's constituted by hydrogen and oxygen elements, both of great importance chemistry and fundamental to human life. Although there are many studies about your physical and chemical properties in the scientific literature, much can be studied yet about this substance. In this study we report the electrical and dielectric properties of the water in liquid phase, such as impedance, dielectric permittivity and dipole moment as a function of frequency (1-20 kHz) in the temperature range between 288 and 314 K. The impedance and dielectric permittivity measurements were carried out in experimental apparatus equipped with an impedance analyzer. In addition, a capacitive system of parallel plate was and entire experiment was shielded to minimize electromagnetic interference effects (noise), and connected to the grounding of the laboratory electrical network. The dipole moment values were estimated applying the Kirkwood's theory based on the definition of Onsager's local field for polar liquids.
Considerando as várias dificuldades dos alunos de Ensino Fundamental em aprender conceitos de físicos, nota-se a necessidade de elaborar novas estratégias de ensino visando minimizar tais dificuldades e, ao mesmo tempo, despertando interesse do aluno para o estudo de Física. Como proposto por Joseph Novak, o mapa conceitual é uma ferramenta utilizada como recurso para alcançar a aprendizagem significativa, contribuindo à construção hierárquica dos conceitos a partir dos conhecimentos prévios dos alunos. Por isso, o presente trabalho foi realizado para abordar a utilização de mapas conceituais como instrumento de avaliação durante o processo de ensino e aprendizagem sobre conceitos de ondas, som e luz. Os mapas conceituais foram elaborados e aplicados aos alunos de uma turma do 9° ano de uma escola pública da cidade de Marabá (Pará). A análise foi baseada em critérios, como segue: conceitos sobre o conteúdo, hierarquização, relações entre os conceitos e clareza durante a leitura do mapa conceitual. A partir dessa análise, observou-se inicialmente que os alunos apresentam grandes dificuldades, e elas diminuem à medida que os mapas conceituais são refeitos. Os resultados deste trabalho permitiram constatar, também, que a ferramenta de mapa conceitual pode ser usada como estratégia de avaliação, bem como observar as limitações e as potencialidades que os alunos apresentam sobre a aprendizagem dos conceitos propostos. Além disso, conclui-se que os mapas possibilitam melhor aprendizagem e valorizam os conhecimentos pré-existentes dos alunos.
A carbon composite electrode modified with copper (II) phosphate immobilized in a polyester resin (Cu 3 (PO 4 ) 2 -Poly) was proposed for the voltammetric determination of catechin in teas. The modified electrode allows the determination of catechin (CAT) at lower potential than that observed at an unmodified electrode. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon composite composition, pH of electrolyte, and others were investigated. The peak current was proportional to the concentration of catechin in the range from 9.9 Â 10 À8 to 1.2 Â 10 À6 mol L À1 , with a detection limit of 5.8 Â 10 À8 mol L À1 . The stability and repeatability of the electrode for the determination of catechin were discussed, and the modified electrode was applied with success in the determination of catechin in teas.
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