Development And Certification Of Synthetic Zinc Isotopic Reference Materials

The development, uncertainty evaluation and certification of eleven newly developed zinc isotope ratio reference materials (GBW04465-04475) are described. The reference materials were gravimetrically prepared with enriched isotopic materials. During the certification, calibrated MC-ICP-MS measrements were performed. The improved techniques for certification in this study are as follows: (a) the isotopic compositions of purified enriched isotopes used for preparation of synthetic isotopic mixtures were obtained by total evaporation-TIMS instead of the traditional iteration method; and (b) the mass discrimination effect in MC-ICP-MS was investigated through a series of isotopic mixtures with a wide range of isotopic compositions, and a non-linearity effect of K factors was observed, and a new correction proposal was employed. The reference materials were certified with a point-to-point proposal instead of the traditional mean and stable K method. Further, the uncertainties were evaluated in detail, and contributions from characterisation, homogeneity and long-term stability were taken into consideration. Among them, contributions from characterisation were particularly detailed: any budgets, for example, weighing and impurity checking, were clearly addressed, and the combined uncertainties were derived by a mathematical differentiation method. In addition, the traceability chain was established, directly pointing to the SI unit, the mole, and a between-laboratory comparison was carried out to validate the reference values.