Desenvolvimento de um método empregando HPLC-HG-AFS para especiação de arsênio em arroz e uso de hidróxido duplo lamelar incorporado com nitroprussiato para adsorção de arsênio

Abstract

Arsenic contamination in food and potable water is of worldwide concern, due to the toxic effects of the substance in humans. Chapter 2 of this work describes the development of a method using high performance liquid chromatography coupled with hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS) for the determination and speciation of the inorganic and organic forms of arsenic most commonly found in rice samples: arsenate (As(V)), arsenite (As(III)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). The best chromatographic resolution was obtained at pH 6.2, using a mobile phase concentration of 20 mmol L-1 and flow rate of 0.57 mL min-1, 5.55% v/v HCl, and 0.90% m/v NaBH4. The accuracy of the method was confirmed by the low relative error values obtained in analysis of a certified reference material (NIST 1568b): 6.63% total inorganic As, 3.44% DMA, 0% MMA, and 0.53% total As. The proposed method presented satisfactory recoveries of 100.8% and 102.1% for rice samples A and H, respectively. Chapter 3 describes a novel procedure for the removal of As(III), As(V), and DMA from water using a lamellar double hydroxide combined with nitroprusside (DLH-NP). The material was found to be selective for arsenic species, as a function of pH. At pH 2.00, all the As(V) was adsorbed, together with part of the DMA (25%). At pH 6.02 and pH 12.00, only As(III) and As(V) were adsorbed, with greater potential for the adsorption of As(V). For the adsorption of As(V) on LDH-NP at pH 2.00 and 6.02, the Langmuir model provided the best fit to the experimental data R² = 0.9996 and 0.9501, respectively. The maximum adsorption capacity (qmax) (77.63 and 18.84 mg g-1) are in agreement with the value obtained experimentally (76.9 and 18.0 mg g-1), respectively. At pH 12.00, the Freundlich model provided the best fits, with R² values of 0.9912. The kinetics of the process showed that the adsorption was favorable as the time for removing As (V) using LDH-NP is low (less than 30 minutes).