High‐Precision Measurement of Molybdenum Isotopic Compositions of Selected Geochemical Reference Materials

Abstract

Here we describe high‐precision molybdenum isotopic composition measurements of geological reference materials, performed using multi‐collector inductively coupled plasma‐mass spectrometry ( MC ‐ ICP ‐ MS ). Purification of Mo for isotopic measurements was achieved by ion exchange chromatography using Bio‐Rad AG ® 1‐X8 anion exchange resin. Instrumental mass bias was corrected using 100 Mo‐ 97 Mo double spiking techniques. The precision under intermediate measurement conditions (eighteen measurement sessions over 20 months) in terms of δ 98/95 Mo was 0.10‰ (2 s ). The measurement output was approximately four times more efficient than previous techniques, with no compromise in precision. The Mo isotopic compositions of seven geochemical reference materials, seawater ( IAPSO ), manganese nodules ( NOD ‐P‐1 and NOD ‐A‐1), copper‐molybdenum ore ( HV ‐2), basalt ( BCR ‐2) and shale ( SGR ‐1b and SC o‐1), were measured. δ 98/95 Mo values were obtained for IAPSO (2.25 ± 0.09‰), NOD ‐P‐1 (−0.66 ± 0.05‰), NOD ‐A‐1 (−0.48 ± 0.05‰), HV ‐2 (−0.23 ± 0.10‰), BCR ‐2 (0.21 ± 0.07‰), SC o‐1 (−0.24 ± 0.06‰) and SGR ‐1b (0.63 ± 0.02‰) by calculating δ 98/95 Mo relative to NIST SRM 3134 (0.25‰, 2 s ). The molybdenum isotopic compositions of IAPSO , NOD ‐A‐1 and NOD ‐P‐1 obtained in this study are within error of the compositions reported previously. Molybdenum isotopic compositions for BCR ‐2, SC o‐1 and SGR ‐1b are reported for the first time.