All at sea with vanadium: Measuring the ratio of vanadium isotopes in seawater

Date: Dec 11, 2018

Chemical proxy

Up to now, the metallic element vanadium has proved of most use as a steel additive that can greatly increase the strength of steel alloys. But, like many transition metals, it is also beginning to find use as a chemical proxy. This is because it has two different stable isotopes – vanadium-51, which is the main isotope, and vanadium-50 – that take part in oxidation and reduction reactions at different rates. As such, the ratio of the two isotopes in ocean sediments can be used as a measure of past oxygen levels.

To be really useful, however, the ratio of vanadium isotopes in ocean sediments needs to be pegged against the ratio in today’s oceans, especially if that ratio differs in different parts of the world, but determining this has proved difficult. Not only is vanadium only present in seawater at fairly low concentrations, but seawater also contains many compounds and elements that can interfere with the detection of the vanadium isotopes. This is especially the case for compounds such as sulfur monoxide (SO) and specific isotopes of the elements chromium and titanium, which all have an atomic mass of 50.

But by taking advantage of ion-exchange chromatography, a team of US scientists, led by Jeremy Owens at Florida State University, has now managed to come up with an efficient method for determining the ratio of the two vanadium isotopes in seawater. Still, the difficulty of doing this meant they had to take advantage of ion-exchange chromatography three times rather than just once.

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