Isotopic delta values of molybdenum standard reference and prepared solutions measured by MC-ICP-MS: Proposition for delta zero and secondary references

We report the isotopic composition of five molybdenum (Mo) standard reference solutions and four fractions from one of these solutions eluted through anion resin column relative to a sixth reference solution. The reference solutions were National Institute of Standards and Technology (NIST) SRM 3134 (lot#891307), Johnson Matthey Specpure (JMC)-Mo Sie (lot#602332B), JMC-Mo Wen (lot#13989C), Merck (lot#170334), Sigma-Aldrich (lot#207306) and Prolabo. Measurements were conducted using Isoprobe multi collector inductively coupled plasma mass spectrometer (MC-ICPMS) at the Centre de Recherches Petrographiques et Geochimiques (France) and Nu Plasma MC-ICPMS at either the Ecole Normale Superieure de Lyon (France) or the Laboratory of Isotope Geology in the Ministry of Land and Resources ( China). The sample-standard bracketing method was employed to correct the mass bias for Mo isotopes during instrumental measurement. Except for the Merck Mo solution, all the Mo solutions were identical in isotopic composition within error. Although the JMC Mo solution has been used as the internal reference material by various groups, uncertainty may still occur with different lot numbers and availability might be limited. Here, we propose the NIST 3134 Mo solution as a new candidate for delta zero reference material, used for reporting Mo isotopic composition of natural samples. Isotopic compositions for four eluted fractions of the Sigma-Aldrich Mo solution were 2.18 parts per thousand, 0.98 parts per thousand, -1.10 parts per thousand and -1.95 parts per thousand for delta Mo-97/95 relative to the NIST Mo standard. These values span the range of reported isotopic compositions for natural terrestrial and experimental samples (approximately -0.5 parts per thousand to 1.6 parts per thousand for delta Mo-97/95). We propose these eluted fractions to be used as a secondary reference for Mo isotope measurements. Mo solutions are available at CRPG upon request.