The 5th International Conference of Geobiology

Molybdenum (Mo) isotopes in sedimentary records have emerged as a robust geochemical proxy for reconstructing paleo-environmental information of the ocean-atmosphere system. Among various sedimentary archives, carbonates present unique analytical challenges due to their exceptionally high matrix elements coupled with extremely low Mo concentration (typically below 1 μg g^-1), which poses significant difficulties in achieving high precision and accurate determinations of Mo isotopic compositions, requiring sophisticated analytical methodologies and rigorous separation protocols. In this study, we developed an innovative analytical protocol combining an efficient pre-enrichment method with a double-stack column chromatographic purification procedure. The optimized pre-enrichment technique demonstrates exceptional performance in quantitative removal of matrix elements, particularly Ca, Mg, and Al, while maintaining Mo recovery rate of approximately 100%. Mo isotopic compositions were determined using a Neptune Plus MC-ICP-MS, with implementation of both the double spike technique and standard-sample bracketing method to rigorously correct for mass fractionation during chemical purification and instrumental analysis. Our proposed procedure was validated through analysis of three reference materials (GSR 1, GSR 2 and GSR 6), yielding δ^98/95Mo_{NIST 3134} values of 0.10 ± 0.07‰ (n=8, 2SD), -0.32 ± 0.04‰ (n=8, 2SD) and 0.30 ± 0.06‰ (n=7, 2SD), respectively. The developed method offers significant advantages in terms of cost-effectiveness and time efficiency, thereby substantially enhancing our analytical capability for Mo isotope geochemistry investigations in carbonates.
 

molybdenum isotopes,carbonates,MC-ICP-MS