δ 98/95Mo values and Molybdenum Concentration Data for NIST SRM 610, 612 and 3134: Towards a Common Protocol for Reporting Mo Data

Abstract

Molybdenum concentration and δ 98/95Mo values for NIST SRM 610 and 612 (solid glass), NIST SRM 3134 (lot 891307; liquid) and IAPSO seawater reference material are presented based on comparative measurements by MC-ICP-MS performed in laboratories at the Universities of Bern and Oxford. NIST SRM 3134 and NIST SRM 610 and 612 were found to have identical and homogeneous 98Mo/ 95Mo ratios at a test portion mass of 0.02g. We suggest, therefore, that NIST SRM 3134 should be used as reference for the δ-Mo notation and to employ NIST SRM 610 or 612 as solid silicate secondary measurement standards, in the absence of an isotopically homogeneous solid geological reference material for Mo. The δ 98/95Mo JMC Bern composition (Johnson Matthey ICP standard solution, lot 602332B as reference) of NIST SRM 3134 was 0.25±0.09‰ (2s). Based on five new values, we determined more precisely the mean open ocean δ 98/95Mo SRM 3134 value of 2.09±0.07‰, which equals the value of δ 98/95Mo JMC Bern of 2.34±0.07‰. We also refined the Mo concentration data for NIST SRM 610 to 412±9μg g -1 (2s) and NIST SRM 612 to 6.4±0.7μg g -1 by isotope dilution. We propose these concentration data as new working values, which allow for more accurate in situ Mo determination using laser ablation ICP-MS or SIMS. © 2012 The Authors. Geostandards and Geoanalytical Research © 2012 International Association of Geoanalysts.