Speciation of inorganic arsenic in rice using hydride generation atomic absorption spectrometry (HG-AAS)

Abstract

Inorganic arsenic (iAs) concentration in rice is a current concern worldwide. A method for iAs determination in rice using hydride generation atomic absorption spectrometry (HG-AAS) is proposed. Arsenic species were extracted from rice using 0.14 mol L⁻¹ HNO₃ assisted by microwave radiation or 0.28 mol L⁻¹ HNO₃ and heating in a water bath prior to As determination by HG-AAS. Selective generation of arsine of As(III) was achieved with 0.1% (m/v) NaBH₄ and 10 mol L⁻¹ HCl. iAs was determined by pre-reduction of all inorganic arsenic and determination under the same conditions used for As(III). By difference, the concentration of As(V) was estimated. Ascorbic acid (1% m/v) and KI (0.2% m/v) in the presence of 1.2 mol L⁻¹ HCl were used for As pre-reduction. The limit of detection (LOD) of As(III) was 1.96 ng g⁻¹ and that of iAs was 3.85 ng g⁻¹, which are feasible for As(III) and iAs speciation in rice. The accuracy was evaluated by analyte recovery tests and analysis of certified reference rice. Total arsenic (tAs) was quantified using alkaline extraction with K₂S₂O₈ and HNO₃, followed by As detection by HG-AAS. Thirteen samples of different types of rice (polished, brown, organic, and parboiled) grown in southern Brazil were analyzed. The iAs, As(III) and As(V) concentrations found were consistent with those already reported for rice.