Meterology of Determination for a New Cadmium Atomic Weight and Metrological Application to Cadmium in Rice Using MC-ICP-MS

Natural cadmium is a chalcophile and highly volatile element and consists of eight stable isotopes. The values of the uncertainties for the isotope abundances have been assessed by the IUPAC and amount to 0.9%~4.8%. Therefore, the determination of a new and improved atomic weight value for natural abundance cadmium has to be in accordance with the IUPAC CAWIA conditions and steps. These conditions and steps are purification of isotopically enriched and natural abundance cadmium by high vacuum metal distillation, determination and calculation of the amount in the metallic and no metallic impurity mass fractions, gravimetric preparation of isotopic mixtures by metrological weighing, determination of isotope ratios of cadmium by multicollector inductively coupled plasma mass spectrometry (MC ICP MS) and thermal ionization mass spectrometry (TIMS), calculation of the atomic weight including evaluation of its combined uncertainty. Some national reference laboratories have now obtained the values for the cadmium amount content in rice. A key comparison reference value is 14.48±0.087 nmol·g -1 .