Desenvolvimento de métodos de extração em fase sólida para especiação de cromo e arsênio empregando sementes de Moringa oleífera como bioadsorvente

Abstract

This work describes the development of solid phase extraction methods for metal ions speciation with emphasis on chromium and arsenic, using Moringa oleifera seeds and their husks as bioadsorbents. Initially, characterization techniques including infrared spectroscopy, thermal analysis, scanning electron microscopy, energy dispersive spectroscopy and study of surface areas by theory adsorption multielement were used in physic chemical evaluation of husks and Moringa oleífera seeds. Subsequently, it is presented the development of flow system for extraction/preconcentration of Cr(III) and Cr(VI) species coupled to the spectrophotometry flame atomic absorption for determination of these species in food and environmental samples. The system is based on the selective retention of Cr(III) and Cr(VI) species in mini- columns filled with husks of the Moringa oleifera seeds. Chemical and flow variables were evaluated using the multivariate method. The retention of Cr(III) occurs in the approximately pH 7,0, and the Cr(VI) retention was approximately pH 1-2. The results of the optimized conditions, selected with the compromise between sensitivity and sample throughput were sample flow rate 4.5 mL min -1 , eluent flow rate of 4.0 mL min-1 ; eluent concentration of 0.01 mol L- 1 the HCl for Cr (III) desorption and 0.01 mol L-1 NaOH to Cr(VI) desorption. The detection limit was 1.9 mg L-1 for Cr (III) and 2.45 g L-1 for Cr (VI). The linear response range was from 5.73 to 1000 mg L- 1 for Cr ( III ) and 7.35 to 1000 mg L-1 for Cr ( VI ) . In order to validate the proposed method , it was applied to water and alcohol samples, as well as the analysis of standard certificate. The study carried out demonstrated the feasibility of using Moringa oleifera husks in flow systems for separation and pre- concentration of chromium species. At the end of the work presents the development of a method for selective extraction of arsenic inorganic species of and detection by Atomic Absorption Spectroscopy Graphite Furnace. The method is based on the selective retention of inorganic arsenic species using as the bioadsorbent Moringa oleifera seeds, the pH being variable to the separation process. At pH 7.0 this As (III )species is quantitatively retained by the seed while the adsorption of As( V) occurs to a lesser extent . The variables that affect the adsorption: mass and contact time were studied, having been found values of 1.0 g and 60 minutes as optimized values . The process of As (III) adsorption of the seeds was studied by starting the construction of adsorption isotherms. The method was applied to the speciation analysis of inorganic arsenic in water samples and evaluated the accuracy of the method based on the analysis of reference material. The values obtained showed high agreement with the actual values , demonstrating the efficiency of the proposed method.