Slurry Sampling and HG AFS for the Determination of Total Arsenic in Rice Samples

Abstract

This paper proposes a procedure for the determination of total arsenic in rice using slurry sampling and hydride generation atomic fluorescence spectrometry (HG AFS). During optimization, water, hydrochloric acid, and nitric acid solutions were tested as extractor. Best results were found using 2.0 mol L⁻¹ nitric acid solutions. The slurries are prepared using 200 mg of rice sample, 5.0 mL of nitric acid solution, and sonication for 30 min. Then, an aliquot of 5.0 mL of the slurry was taken and 3.0 mL of 1.5 mol L⁻¹ hydrochloric acid solution and 1.5 mL of 10 % potassium iodide in 2 % ascorbic acid solution were added. After 30 min, the volume was completed up to 10 mL with ultra-pure water and arsenic quantified by HG AFS. In these experimental conditions, the method allows the determination of arsenic employing external calibration, with limits of detection and quantification of 1.1 and 3.3 ng g⁻¹ and precision expressed as relative standard deviation (%RSD) varying between 5.9 and 1.3 % for arsenic concentration of 0.12 and 0.47 μg g⁻¹. Accuracy was confirmed by analysis of the NIES standard reference material for rice flour, SRM 10b. This method was used to determine the arsenic content in 20 rice samples that were purchased at supermarkets in Salvador, Bahia, Brazil. The arsenic content for the three types of rice (white, parboiled, and brown) varied from 0.12 and 0.47 μg g⁻¹. Some of the samples were also analyzed by HG AFS after complete mineralization in block digester employing a reflux system (cold finger). A statistical test showed that there was no significant difference between the results obtained using slurry sampling and those obtained after complete digestion of the sample.