ARSENIC SPECIES IN RICE

Rice is the primary source of energy for 50% of the world's population, the second most produced cereal after corn. For other cereals, rice has arsenic levels at least ten times higher and is considered the main source of arsenic in the diet of those countries with low levels of arsenic in drinking water. Due to the occurrence of arsenic in rice and that the toxicity of inorganic species (As+3 and As+ 5) is much higher than that of the organic species Dimethyl Arsenic (DMA) and Mono Methyl Arsenic (MMA) the Codex Alimentarius has established the maximum allowable limit for arsenic inorganic species in polished and husked rice (0.20 and 0.35 mg/kg respectively). In order to comply with these new requirements, the implementation and validation according to ISO 17025:2005 of an arsenic rice speciation technique is proposed by means of a coupled High Pressure Liquid Chromatograph (HPLC) with Atomic Emission Spectrometer with detection of Masses (ICP-MS) in samples of polished and husked rice. The Arsenic Speciation in Rice and Rice Products Using High Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometric Determination method was used. Elemental Analysis Manual for Food and Related Products (FDA 4.11); For the determination of inorganic arsenic (as a sum of species As+ 3 and As+5) and of DMA and MMA, most species in rice, a Perkin Elmer Flexar HPLC coupled to a Perkin Elmer Nex Ion 350 D Mass Spectrometer was used. A modification to the recommended working pH should be introduced. In addition, peak splitting was observed in the resolution of the MMA in spiked matrix, which did not prevent the quantification of arsenic as a sum of species. The recoveries obtained from inorganic As were in the order of 110% and of total As as sum of species of 92% for the reference materials NMIJ CRM 7532 Brown Rice Flour and NIST 1568 b Rice Flour. The results obtained from total arsenic by HPLC-ICPMS were compared for commercial rice samples (n = 20) against the traditional methodology [Atomic Absorption Spectrometry with Electrothermal Atomization (ETAAS) and Sample Treatment by Microwave Digestion (AOAC Method 999.10:2005 adapted)], finding that the average recovery is 0.81 of total arsenic in one technique over the other. For the above, the method chosen was adequate for the determination of inorganic As in rice and showed promising results for the determination of total As as a sum of major species.