Determination of trace elements in rice flour by isotope dilution inductively coupled plasma mass spectrometry

Two rice flour reference materials (normal and elevated trace concentrations) were prepared from brown rice produced in Korea. As part of the certification process, trace elements such as Cr, Fe, Cd and Pb were determined by an isotope dilution ICP-MS method. About 0.4 g of rice flour samples spiked with appropriate amounts of enriched spike isotopes was decomposed in high-pressure microwave digestion bombs. For the determination of Cr and Fe, the ICP-MS instrument employed in the present work was operated under cool plasma conditions. The cool plasma was generated by inserting a copper shield between the load coil and the plasma, and by increasing the aerosol carrier gas dow rate up to 1.31 min(-1). An approximately 2 mu g ml(-1) Ca matrix in the digested solution was observed to induce serious spectral interference on the determination of Fe; hence, the Ca matrix was separated from the analyte using a microcolumn loaded with silica-: immobilized 8-hydroxyquinoline. Analytical results for National Institute of Standards and Technology Standard Reference Material 1568, Japan National Institute for Environmental Studies Certified Reference Material 10-a and Korea Research Institute of Standards and Science reference materials are presented together with detection limits.