Especiação de arsênio em meio aquoso através da imobilização de As(III) e As(V) em diferentes sistemas de extração em fase sólida

Abstract

The study of the arsenic speciation has become an essential tool for the assessment of the toxicological effects and bioavailability of arsenic species in aqueous environment. One of the most important steps for an efficient arsenic speciation is the sample preparation, which requires the preservation of the original arsenic compounds and their oxidation state. Among the methods used for sample preparation, the solid phaseextraction (SPE) can be considered as the most commonly applied sample handling technique. In this work, a new system for inorganic arsenic speciation was developed using a thiol chelating resin packed into a disposable syringe. In this system, As(III) is the immobilized species, in contrast to other SPE cartridges currently available, whichremove the pentavalent species. The performances of two SPE cartridges for inorganic arsenic speciation were evaluated: a silica-based anion exchange cartridge, LC-SAX (Supelco, PA Bellefonte), and a tailor-made cartridge filled with the Amberlite GT73 resin (Rohm and Haas), a thiol chelating resin. The As removal and selectivity of these cartridges were assessed under different conditions of pH, flow rate and in thepresence of competing species. The characterization of the two resins loaded with arsenic was carried out using X-ray Absorption Spectroscopy. The different oxidation state of the adsorbed species by the two resins was demonstrated by XANES (X-ray absorption near edge structure) analyses. In addition, EXAFS (Extended X-ray absorption fine structure) resolved the molecular structure of sorbed arsenic onto the Amberlite GT73 loaded resin, showing a coordination of one atom of arsenic with three sulfur atoms. Both the LC-SAX and Amberlite GT73 cartridges were able to efficiently separated the inorganic arsenic species, As(V) and As(III), in a broad pH range (above 2.1 for LC-SAX and below 10 for Amberlite GT73), and at flow rates up to 5.0mL min-1. The presence of competing ions have not altered the As(III) and As(V) immobilizationby the Amberlite GT73 and LC-SAX cartridges, except when 250 mg L-1 of sulfate was used. However, the selectivity of both resins was significantly affected by the presence of sulfate and phosphate ions, as well as iron (Fe2+ and Fe3+) in the experiments with Amberlite GT73. The present results show that the developed protocol using Amberlite GT73 resin can be applied for arsenic speciation in surface waters for both laboratoryand field work purposes, thus arising as a novel alternative for As(III) speciation and a useful complement to the available anion exchange methods.