Determination Method for Total Arsenic and Partial-digestion Method with Nitric Acid for Inorganic Arsenic Speciation in Several Varieties of Rice

Abstract

The determination method of total arsenic (As) and the speciation method of inorganic As for non-glutinous rice reported in our preceding paper were applied to several varieties of rice under optimized experimental conditions. In the determination of total As with ICP-MS, acetic acid was added to increase the sensitivity and an internal reference method with germanium was adopted to increase the precision. The extraction temperature in the partial-digestion method with nitric acid to speciate inorganic As was raised to 100ῌ, because extraction e$ciency over 90῍ was obtained from glutinous rice and colored rice at this temperature. In the investigation of polished and unpolished forms of non-glutinous, glutinous, and colored rice, the amounts of total and inorganic As were 0.04ῌ0.54 mg/kg and 0.02ῌ0.41 mg/kg, respectively. The color of rice was not related to total or inorganic As content. These results indicate that the inorganic As content in commercial rice should be carefully monitored.

Determination of Sixteen Elements and Arsenic Species in Brown, Polished and Milled Rice

“…Arsenic species were extracted from the prepared rice flour samples using a heating-block extraction technique with HNO3 as the solvent. 30,31 A portion of each sample (0.5 g) was placed in a 10-mL glass tube, and 2 mL of 0.15 mol L -1 HNO3 was added. The capped tube was placed in a heating block at 100 C for 2 h. After cooling, a small volume of water was added, and the tube was centrifuged at 3500 rpm for 10 min.…”

Non-chromatographic Speciation of Inorganic Arsenic in Rice by Hydride Generation Inductively Coupled Plasma Optical Emission Spectrometry

“…As it was shown, the selected procedure for i-As determination in rice (P5), although was not applicable for DMA, the response for MMA reached in these conditions nearly 50% of this achieved for As(III,V) species. On the other hand, it should be honestly stated that As in rice is mostly present as i-As and DMA (Huang et al 2015;Narukawa et al 2014;Nishimura et al 2010;Raber et al 2012). MMA is found occasionally and its concentration is typically low (< 30 ng g −1 (d.w.)) or quite often undetectable, i.e., < 8 ng g −1 (Huang et al 2015;Narukawa et al 2014;Nishimura et al 2010;Petursdottir et al 2014;Raber et al 2012).…”

“…Toxicity of As depends on its individual species and four potentially toxic As forms, i.e., inorganic arsenicals (i-As), namely arsenite and arsenate [As(III,V)], in addition to methylated compounds, i.e., o-As, represented by dimethylarsenate and monomethylarsonate (DMA, MMA) are present in rice. Their levels are variable but i-As and DMA are predominant species (Huang et al 2015;Narukawa et al 2014;Nishimura et al 2010;Raber et al 2012). Nevertheless, despite being recognized as the minor organic form of As in rice, MMA has also been determined at very low concentrations, i.e., < 30 ng g −1 of dry weight (d.w.) (Huang et al 2015;Petursdottir et al 2014;Raber et al 2012).…”

Preparation of arsenic‐containing white rice grains as calibration standards for X‐ray fluorescence analysis of total arsenic in cereals

“…The predominant As species in rice are As(III), As(V), and dimethylarsinic acid (DMA) . Rice containing other As species such as monomethylarsonic acid, arsenocholine, and arsenobetaine has been reported in the literature. The toxicity level of As depends on its chemical form; for example, As(III) is more toxic than As(V) and organic As is less harmful to humans than inorganic forms .…”

“…In general, speciation analysis of As in rice is carried out by HPLC/ICP‐MS after the extraction of As species into a solvent such as nitric acid (HNO 3 ) or deionized water . However, for the accurate evaluation of As species in rice and their toxicity by extraction, it is necessary to optimize the extraction conditions for each sample.…”