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Published September 2, 2013 | public
Journal Article

A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry

Abstract

The study of Fe, Zn and Cd stable isotopes (δ^(56)Fe, δ^(66)Zn and δ^(114)Cd) in seawater is a new field, which promises to elucidate the marine cycling of these bioactive trace metals. However, the analytical challenges posed by the low concentration of these metals in seawater has meant that previous studies have typically required large sample volumes, highly limiting data collection in the oceans. Here, we present the first simultaneous method for the determination of these three isotope systems in seawater, using Nobias PA-1 chelating resin to extract metals from seawater, purification by anion exchange chromatography, and analysis by double spike MC-ICPMS. This method is designed for use on only a single litre of seawater and has blanks of 0.3, 0.06 and <0.03 ng for Fe, Zn and Cd respectively, representing a 1–20 fold reduction in sample size and a 4–130 decrease in blank compared to previously reported methods. The procedure yields data with high precision for all three elements (typically 0.02–0.2‰; 1σ internal precision), allowing us to distinguish natural variability in the oceans, which spans 1–3‰ for all three isotope systems. Simultaneous extraction and purification of three metals makes this method ideal for high-resolution, large-scale endeavours such as the GEOTRACES program.

Additional Information

© 2013 Elsevier B.V. Received 8 March 2013. Received in revised form 24 May 2013. Accepted 8 July 2013. Available online 15 July 2013. We would like to thank Frank Wombacher and Derek Vancefor providing Cd and Zn isotope standards, Ken Bruland and Geoff Smith at UCSC for supplying SAFe standards, Beth Bair at the University of South Carolina for technical support, Paul Field at ESI foruseful discussions on methane, and the Captain and Crew of the R.V. Knorr for collecting samples for us on the US GEOTRACES A03 Transect and the IC1 GEOTRACES cruises. We would also like to thank two anonymous reviewers for their helpful comments. The University of South Carolina and NSF Grant OCE-1131387 funded this study.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023