Simultaneous preconcentration of 9Be and cosmogenic 10Be for determination of the 10Be/9Be ratio in (coastal) seawater

Abstract

Beryllium isotopes have emerged as a quantitative tracer of continental weathering, but accurate and precise determination of the cosmogenic ¹⁰Be and stable ⁹Be in seawater is challenging, because seawater contains high concentrations of matrix elements but extremely low concentrations of ⁹Be and ¹⁰Be. In this study, we develop a new, time-efficient procedure for the simultaneous preconcentration of ⁹Be and ¹⁰Be from (coastal) seawater based on the iron co-precipitation method. The concentrations of ⁹Be, ¹⁰Be, and the resulting ¹⁰Be/⁹Be ratio for Changjiang Estuary water derived from the new procedure agree well with those obtained from the conventional procedure requiring separate preconcentration for ⁹Be and ¹⁰Be determinations. By avoiding the separate preconcentration, our newly developed procedure contributes toward more time-efficient handling of samples, less sample cross-contamination, and a more reliable ¹⁰Be/⁹Be ratio. Prior to this, we validated the iron co-precipitation method using artificial seawater and natural water samples from the Amazon Estuary regarding: (1) the “matrix effect” for Be analysis, (2) its extraction efficiency for pg g⁻¹ levels Be in the presence and absence of organic matter, and (3) the data comparability with another preconcentration method. We calculated that for the determination of ⁹Be and ¹⁰Be in most open ocean seawater with typical ¹⁰Be concentrations of > 500 atoms g⁻¹, good precisions (< 5%) can be achieved using less than 3 liters of seawater compared to more than 20 liters routinely used previously. Even for coastal seawater with extremely low ¹⁰Be concentration (e.g., 100 atoms g⁻¹), we estimate a maximum amount of 10 liters to be adequate.