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.

Automated summary

This study describes the development, uncertainty evaluation, and certification process of eleven newly developed zinc isotope ratio reference materials. Improved techniques were used for the certification process, detailed uncertainties were evaluated, and a traceability chain was established to validate reference values through between-laboratory comparisons.