Determination method for total arsenic and partial-digestion method with nitric acid for inorganic arsenic speciation in several varieties of rice.

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 100°C, because extraction efficiency 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 0.04-0.54 mg/kg and 0.02-0.41 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.