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Other Titles: Spectrophotometric determination of methylene blue presence of Green Malachite antiparasitic use in veterinary
Keywords: azul de metileno;  verde de malequita;  determinação espectrofotométrica;  determinação cromatográfica;  cinética;  Methylene blue;  malachite green;  spectrophotometric determination;  chromatographic determination;  kinetic;  Corante;  Espectrofotometria;  Cromatografia;  Cinética química (química orgânica);  dye;  spectrophotometry;  chromatography;  chemical kinetics (organic chemistry)
Issue Date: 29-Feb-2012
Abstract: The use of veterinary products without proper licensing (irregular products) can be dangerous for the animal, to the applicator and the people who consume food from treated animals (meat, milk, eggs, fish and honey). Methylene blue (MB) and malachite green (MG) are on the list of veterinary products irregular Ministry of Agriculture, Livestock and Supply (MAPA). These dyes have been widely used as topical antiseptics in the treatment of infections by parasites, fungi and bacteria in fish and their eggs, representing a significant health risk for people who eat contaminated fish or even go in some way, in contact with such substances. Due to its ease and low cost of production, they are still used in some countries with less restrictive laws, even in fish farms for human consumption. Experiments to evaluate the spectrophotometric behavior of aqueous solutions of the two dyes depending on the pH (3.00 to 11.00) were performed. It was observed that in all investigated pH values a partial overlap of the absorption spectra of the two substances occurred, with coincident absorption maxima, making difficult their determination by the method of absorption addition. The bleaching alkaline solutions of malachite green was also observed at pH 11.00, following a first-order kinetics governed by the equation ln [MG] = ln [MG] 0 - kt (k = 0,25 min- 1). This discoloration was explored to eliminate the overlapping spectra of both dyes, and the analyte (MB) is determined spectrophotometrically at λ = 663 nm, after solution bleaching during 30 minutes. Studies using the analytical curve of methylene blue allowed evaluation of the interference in the determination of MG before the bleaching solution. This interference has been removed by bleaching MG (30 minutes at pH 11.00), comparison of the curves with MB obtained in aqueous solutions, solutions containing VM after bleaching, and using the standard addition confirmed the possibility of using the curve the analytical measurement, since the comparison of the angular coefficients indicated that there was no interference in the decomposition product on curve parameters, nor a matrix effect. Voltammetric studies supported the hypothesis about the interaction between the dyes. They were also quantified by high performance liquid chromatography using UV/Vis-DAD detection. Although there were no agreement between observed and labeled values, comparisons between spectrophotometry and chromatography indicated that both the proposed techniques lead to concentrations of MB that did not differ statistically significant according to a paired t-test at 95% confidence.
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