Especiação química de arsênio em amostras de arroz empregando extração por fase sólida in-situ e determinação por FI-HG AAS

Abstract

In this work a new method for chemical speciation of arsenic in rice samples is proposed, by means of solid phase extraction in situ-based on quaternary ammonium salt and (ISQAS-SPE). Among a large number of publications on arsenic speciation using chromatographic techniques, this method aims to contribute to the state of the art of non-chromatographic speciation, which is still little explored. Inorganic arsenic species after extraction and preconcentration were determined as As (III) by atomic absorption spectrometry with hydride generation in a flow injection analysis system with coalescing zones by multicomputing (FI-HG AAS). The As (III) species selectively complexes with APDC agent at pH 1.0 and they are extracted by the microparticles of the formed solid phase. Tetra-n-butylammonium bromide (TBAB) was used as Phase Transfer Agent while the ClO4- anion was the Ionic Paretic Agent, forming tetra-n-butylammonium perchlorate as the extractive solid phase. Characterization assays revealed particles with micrometric scaling, without a defined morphology and high surface area. The extraction of As(PDC)3 complex occurs by adsorption mechanisms and hydrophobic interactions. The ISQAS-SPE procedure was optimized through factorial design and response surface methodology using Central Compound Design (CCD). Under optimal extraction conditions, the variables influencing the FI-HG AAS determination system were optimized in an univariate form, from which 88% of As (III) recovery efficiency can be obtained. The determination of total inorganic arsenic was possible by pre-reduction step with hydroxylamine hydrochloride 0.5% (m /v), of which the concentration of the As (V) species can be determined by difference. Concomitant interference studies have indicated significant interference of Cd(II) and Mn(II) metal ions, characteristic of interference in liquid phase, of which they can be minimized by the addition of EDTA as masking agent. On the other hand no significant interferences were observed in the methylated species MMA and DMA. It has been found that it is possible to selectively determine the DMA species in the absence of MMA from the HG AAS supernatant solution using acetate buffer pH 5.0 and 0.4% (m /v) NaBH4. The method has potential for the determination of low concentrations of arsenic, with a preconcentration factor of 17. The limits of detection and quantification obtained were respectively 0.040 and 0.12 μg L-1 for total As; and 0.46 and 1.5 μg L-1 for DMA, with an accuracy of 5.5% for As(III) 10.0 μg L-1. The method was applied in IRMM-804 Rice Flour certified reference material obtaining 92% accuracy. The method is simple and shown to be applicable to the monitoring of arsenic in rice samples within the values established by current legislation.