Speciation and determination of inorganic arsenic in rice using liquid chromatography-inductively coupled plasma/ mass spectrometry: collaborative study

An analytical method to speciate two inorganic As forms [arsenite, As(lll) and arsenate, As(V)] in indica and japonica types of rice (both husked and polished) and determine the inorganic As concentration as the sum of these two was internationally validated. The method can additionally determine two organic As compounds, monomethylarsonic acid and dimethylarsinic acid, in rice as separate LC peaks. The method is based on LC separation and inductively coupled plasma (ICP)-MS detection. The method was evaluated through the International Union of Pure and Applied Chemistry/lnternational Organization for Standardization/AOAC harmonized protocol. Sixteen laboratories from four countries participated in the study, and 13 laboratories returned valid data. Twenty test portions of 10 blind duplicates of indica and japonica type rice samples (both husked and polished) were used in this study. Repeatability RSD (RSDr) and reproducibility RSD (RSDR) were calculated at five concentrations of total inorganic As between 0.03 and 0.68 mg/kg. The RSDr was in a range of 3.8 to 7.7% and the RSDR was in a range of 10 to 36%. These performance characteristics were found to be sufficient for determination of inorganic As at or higher than 0.03 mg/kg. Applicability of the method was estimated to be in a range of 0.02-2.0 mg/kg.