In this work, a simple electrochemical biosensor for 4-chlorophenol was developed based on laccase immobilized on a hybrid nanocomposite (ZnO nanoparticles/chitosan), and incorporated in a carbon paste electrode. There are few biosensors in the literature for this specific pollutant because it tends to form polymeric films on the electrode, causing surface passivation or even enzyme inactivation. The carbon paste allowed the surface to be easily renewed by polishing, which amends this limitation. To optimize the experimental conditions, we used cyclic voltammetry and hydroquinone as a representative of phenolic compounds due to the high toxicity of chlorophenol, thus avoiding the generation of hazardous residues. After optimization, a calibration curve was constructed for 4-chlorophenol using differential pulse voltammetry, and a linear response was obtained from 1 to 50 µM, with a lower detection limit of 0.7 µM. The obtained biosensor showed high accuracy when employed in the analysis of industrial wastewater.
Resumo: Concentrações elevadas de glicerina livre em biodiesel causam danos em motores. Pela legislação brasileira, (ANP Resolução 45/2014), o limite máximo permitido para glicerina livre em biodiesel é 0,02 % em massa. A norma ASTM D6584 estabelece que o método padrão para se determinar glicerina livre em biodiesel é cromatografia gasosa, uma técnica demorada e cara. Como alternativa, a glicerina livre pode ser quantificada, após derivatização, por espectroscopia de absorção na região do UV-Visível (410 nm). No presente trabalho usamos o protocolo de validação para o método espectroscópico. Resultados indicam que o método é linear (r 2 = 0.995) para o intervalo de concentrações estudado e possui exatidão e precisão aceitáveis. O método apresentou valores de desvio padrão relativos para repetibilidade e exatidão abaixo de 5,0 %. Para o cálculo dos valores de limite de detecção e quantificação foram empregados três diferentes métodos. Dois deles apresentaram limites de quantificação apropriados para glicerina. Entretanto, o método proposto pelo INMETRO forneceu um valor maior para o limite de quantificação. Considerando que o método é baseado em reação química de derivatização, com parâmetro colorimétrico, a robustez do método foi analisada para pequenas alterações na reação em função da temperatura, do comprimento de onda e do material da cubeta. Os resultados mostraram que o método é robusto para pequenas variações na temperatura de reação, mas não é robusto para mudanças no comprimento de onda e para mudança de material da cubeta (plástico ou vidro).
Phenolic compounds are important environmental contaminants due to their high toxicity and persistence in the environment. The use of enzyme-based electrochemical biosensors is a simple, sensitive and low-cost alternative for the determination of these pollutants in contaminated waters. However, in most cases, it is impossible to detect specific compounds in a mixture of phenols due to signal-overlap, as the instruments operate at very close potentials, given that the system is based on a single enzyme to detect similar structures. In order to overcome this problem, in the present work we have successfully used multivariate calibration with partial least squares (PLS) for the simultaneous determination of hydroquinone and guaiacol by a tyrosinase-based biosensor that was assembled using an enzyme extract from yam. The use of PLS allowed us to work with a large number of voltammograms, leading to a single mathematical model for the simultaneous determination of phenols of similar structure in real samples with concentration values of mmol L -1 .
In this study we propose the use of a natural indicator obtained from the seeds of plant found abundantly in the southern of Bahia, Brazil, Theobroma cacao L. (cocoa). The extract containing the dyes from cocoa seed was applied as indicator in several acid/base titrations, and the results were compared with values obtained in potentiometric titrations and using phenolphthalein as an indicator of reference. The methodologies involving weak and strong acids were applied with chemistry graduate students of
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