Desenvolvimento de métodos não cromatográficos para especiação de selênio empregando ionização por dessorção e extração em fase sólida

Abstract

The study aimed to develop non-chromatographic methods for selenium speciation, organic and inorganic, using desorption methodology and inonização electrospray (DESI) and solid phase extraction (SPE), Moringa oleifera impregnated with thiosemicarbazide. For the studies of analysis with DESI source was used coupled to Mass Spectrometer, and evaluated the temperature of the capillary, the spray voltage, the solvent flow, and testing standards of the species studied: selenomethionine, selenomethylcistine, selenocysteine, selenite and selenate. The method was applied to Brazil-nut samples, cabbage, garlic and spinach. For speciation of selenium in SPE is used Moringa oleifera seeds impregnated with thiosemicarbazide were studied pH, concentration of reactants involved, the adsorption isotherm, adsorbent mass, contact time and optimizations with patterns of selenite and selenate. In addition, the physicochemical characterization of the material and the optimization of detection technique parameters were performed. The results obtained showed minimal detectable amount DESI in the picogram order; all species were detected in the samples except the spinach sample, which was not found selenometilcisteina. All organic species were confirmed by ion fragmentation when compared to standards. In studies of Moringa oleifera was selective removal of Se+4 with 0.25 g of the adsorbent mass, contact time of the adsorbent with the solution for 60 min, concentration of NaBH4 0.5% (w/v), HCl 1 0% (v/v) and pre-reducing L-cysteine was better. Observed was found that at pH = 3.5, the species Se+4 is retained by the seed, while the adsorption of Se+ 6 occurs to a lesser extent. The process of adsorption of the species Se+4 the seed impregnated with thiosemicarbazide was studied from the construction of adsorption isotherms, being adjustable to the models of Languimir and Freundluch. The results of the evaluated parameters are in accordance with the law, and the two methodologies can be employed in selenium speciation. Improvements are needed for quantification in the case of using DESI source for speciation and organic species in the case of SPE studies.