Development of Molybdenum Isotopic Certified Reference Materials with SI-traceable Property Values

Molybdenum isotopes have been widely studied and applied to various fields of Earth and planetary sciences in recent years. Inspired by the increasing demand for reliable and comparable measurement data, three molybdenum isotopic reference materials have been developed by the National Institute of Metrology (China), including one natural-abundance iCRM (GBW 04504) and two isotopically enriched iCRMs of Mo-97 (GBW 04505) and Mo-100 (GBW 04506), respectively. The property values of isotope amount ratios and isotopic abundances of these iCRMs have been certified by fully calibrated mass spectrometry using a multi-collector inductively coupled plasma-mass spectrometer. The instrumental mass bias correction was performed using five synthetic isotope mixtures, which were gravimetrically prepared by all seven high-purity molybdenum isotope materials. The determined absolute molybdenum isotopic compositions of GBW 04504, 04505 and 04506 are thus traceable to the SI units kilogram and mole. On the basis of the assessment in ISO Guide 35: 2017, these iCRMs exhibited sufficient homogeneity and stability for the application of molybdenum isotope-ratio determinations. The delta Mo-98/95(NIST SRM 3134) value of GBW 04504 was measured as -0.31 +/- 0.07 parts per thousand (1s(m)) relative to the delta zero reference material NIST SRM 3134 (Lot No. 130418).

Automated summary

Three molybdenum isotopic reference materials have been developed and certified using fully calibrated mass spectrometry with a multi-collector inductively coupled plasma-mass spectrometer. The absolute molybdenum isotopic compositions of these materials are traceable to the SI units kilogram and mole through instrumental mass bias correction with five synthetic isotope mixtures. These reference materials have exhibited sufficient homogeneity and stability for molybdenum isotope-ratio determinations based on the evaluation in ISO Guide 35: 2017.