Accurate fast screening for total and inorganic arsenic in rice grains using hydride generation atomic fluorescence spectrometry (HG-AFS)

Abstract

Two novel methods based on hydride generation atomic fluorescence spectrometry for the accurate screening of total and inorganic arsenic (As) in rice grain digests in 5 and 2 minutes, respectively, are proposed here. Total As determination was achieved using online UV photolysis aided by alkaline potassium persulphate oxidation, which converted all organic As to arsenate and thus allowed quantitative hydride generation. Determination of inorganic As in rice grains was accomplished by selective hydride generation at high acidity (4.8 M HCl), which allowed ∼50 times higher efficiency for hydride generation of arsenite than the prevalent form of organic As in rice, namely dimethylarsonic acid (DMA), after pre-reduction of all inorganic As using potassium iodide/ascorbic acid. The accuracy of the method was verified by (1) excellent agreement with the certified value of total As and the literature values of inorganic As in NIST SRM 1658a; (2) complete recovery of total As in NIST SRM 1568a spiked with additional 2 ng As g⁻¹ of DMA; (3) excellent agreement of total and inorganic As values in 80 samples of different types, origins and treatments (standing for different matrices) compared to ICP-MS and HPLC-ICP-MS measurements; (4) ∼100% recovery of inorganic As in ERM-BC-211 and a round grain rice sample even spiked with DMA up to 200 ng As g⁻¹. Additionally, the low data dispersion was indicated by the low relative standard deviation (∼4.3%) in the day-to-day precision for quantifying inorganic As in NIST SRM 1568a on 7 different days.