d98/95Mo values and Molybdenum Concentration Data for NIST SRM 610, 612 and 3134: Towards a Common Protocol for Reporting Mo Data

Molybdenum concentration and d98/95Mo 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 0.02 g. We suggest, therefore, that NIST SRM 3134 should be used as reference for the dMo 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 d98/95MoJMC Bern composition (Johnson Matthey ICP standard solution, lot 602332B as reference) of NIST SRM 3134 was 0.25 +/- 0.09 parts per thousand (2s). Based on five new values, we determined more precisely the mean open ocean d98/95MoSRM 3134 value of 2.09 +/- 0.07 parts per thousand which equals the value of d98/95MoJMC Bern of 2.34 +/- 0.07 parts per thousand. We also refined the Mo concentration data for NIST SRM 610 to 412 +/- 9 mu g g-1 (2s) and NIST SRM 612 to 6.4 +/- 0.7 mu g 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.