PP31B-2233
Development of analytical techniques of vanadium isotope in seawater

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Tianyi Huang1, Jeremy D Owens2, Adam Sarafian2, Indra SEKHAR Sen3, Kuo-Fang Huang4, Jerzy Blusztajn5 and Sune Nielsen2, (1)MIT/WHOI Joint Program, Woods Hole, MA, United States, (2)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)WOODS HOLE OCEANOGRAPHIC INSTITUTION, WOODS HOLE, MA, United States, (4)WHOI, Woods Hole, MA, United States, (5)WHOI, Department of Marine Geology and Geophysics, Woods Hole, MA, United States
Abstract:
Vanadium (V) is a transition metal with isotopes of 50V and 51V, and oxidation states of +2, +3, +4 and +5. The average concentration in seawater is 1.9 ppb, which results in a marine residence time of ~50 kyrs. Its various oxidation states make it a potential tool for investigating redox conditions in the ocean and sediments due to redox related changes in the valance state of vanadium. In turn, chemical equilibrium between different oxidation states of V will likely cause isotopic fractionation that can potentially be utilized to quantify past ocean redox states. In order to apply V isotopes as a paleo-redox tracer, it is required that we know the isotopic composition of seawater and the relation to marine sources and sinks of V.

We developed a novel method for pre-concentrating V and measuring the isotope ratio in seawater samples. In our method, we used four ion exchange chromatography columns to separate vanadium from seawater matrix elements, in particular titanium and chromium, which both have an isobaric interference on 50V. The first column uses the NOBIAS resin, which effectively separates V and other transition metals from the majority of seawater matrix. Subsequent columns are identical to those utilized when separating V from silicate samples (Nielsen et al, Geostand. Geoanal. Res., 2011). The isotopic composition of the purified V is measured using a Thermo Scientific Neptune multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) in medium resolution mode. This setup resolves all molecular interferences from masses 49, 50, 51, 52 and 53 including S-O species on mass 50.

To test the new method, we spiked an open ocean seawater sample from the Bermuda Atlantic Time Series (BATS) station with 10-25 μg of Alfa Aesar vanadium solution, which has an isotopic composition of δ51V = 0 [where δ51V = 1000 × [(51V/50Vsample - 51V/50VAA)/51V/50VAA]. The average of six spiked samples is -0.03±0.19‰, which is within error of the true value of 0‰. The average yield of 96% further shows that our method is not associated with any loss of V. Preliminary results for un-spiked BATS seawater samples reveal V isotopic compositions close to that of the AA standard. Further analyses of BATS seawater as well as the NASS-6 seawater reference material are in progress.

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