Emprego da eletroextração multifásica e técnicas espectroscópicas para a determinação de corante azul de metileno em água tratada

Abstract

Methylene blue dye and other compounds are released into water bodies daily and primarily originate from the textile industry and aquaculture. After going through several purification processes at the treatment plants, water intended to be released to the environment or for human consumption may still contain residues of undesirable species, referred to as emerging contaminants, which can cause serious health effects. Therefore, a multiphase electroextraction system for large sample volumes, with a solid support for the acceptor phase, was developed and optimized to extract and pre-concentrate methylene blue dye present in treated water samples. The electroextraction system utilizes a multi-well base, allowing for multiple simultaneous extractions with subsequent analysis by molecular absorption spectrophotometry in the visible region and Raman spectroscopy. The system uses cotton as a support for the acceptor phase, because it showed excellent results in sorption/desorption tests. The best system configuration was achieved with a free organic filter without stirring. A Box-Behnken-type plan was used to optimize the following variables: extraction time, pH, and acetonitrile percentage in the donor phase. The parameters for the electroextraction system were as follows: acceptor phase, 0.0300 g of cotton soaked in 0.50 mol L-1 acetic acid; donor phase, McIlvaine buffer, pH 5,00, 35% (v/v) acetonitrile, 3,00 mL of 1-octanol used as a free organic filter; application of 300 V for 25 min. Using molecular absorption spectroscopy in the visible region, a matrix-matched curve was obtained and linearity was demonstrated in the range of 0.030 to 0.375 mg L-1. The proposed method was validated, achieving precision with a relative standard deviation between 3,0 and 9.9% and a recovery range between 99 and 105%, with detection and quantification limits of 0.001 and 0.004 mg L-1, respectively. No matrix effects were observed and the calculated extraction efficiency was 31% with a 10-times pre-concentration. Qualitative analysis of the Raman spectra allowed the detection of methylene blue dye at concentrations as low as 5 x 10-5 mg L-1. The newly developed method showed agility because multiple extractions could be performed simultaneously, which allowed the analysis of samples with low concentrations of methylene blue due to the high pre-concentration power and selectivity.