Preparation and certification of rice flour-unpolished reference material.

Rice flour-unpolished reference material was prepared from unpolished rice collected from three locations in Japan. This reference material is certified for elemental composition and consists of three samples containing low-level (0.023 microgram/g), medium-level (0.32 microgram/g) and high-level (1.82 micrograms/g) of Cd. The unpolished rice was pulverized, oven-dried, homogenized and finally packaged into 1000 glass bottles. The prepared material satisfied the homogeneity criteria for a reference material. Collaborative analytical studies on the elemental composition of the rice flour-unpolished reference material were conducted using various analytical techniques which lead to the certification. Stable isotope dilution/ICP-MS was successfully applied to the accurate determination of Cu, Zn, Mo and Cd in the reference material. Certified values are provided for Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Rb and Zn, based on results of determinations by at least three independent analytical techniques. Reference values are reported for Al, As, Br, Cl, Co, Cr, Hg, Se and Sr. The elemental compositions of the three rice flour-unpolished samples are very similar, except for Cd, and are considered typical of Japanese unpolished rice.