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Issue 10, 2018
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Synchrotron X-ray spectroscopy for investigating vanadium speciation in marine sediment: limitations and opportunities

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Abstract

Vanadium (V) exists in a number of oxidation states in the environment, potentially making it a useful chemical tracer of both modern and ancient redox conditions in Earth's oceans. However, the use of V as a redox tracer relies on a comprehensive understanding of V geochemistry in marine systems, which in turn requires the ability to accurately measure its solid-phase speciation in marine sediments. Here we report the first evaluation of both bulk and microfocused synchrotron X-ray spectroscopy to investigate the speciation of V in a modern coastal marine sediment. Semi-quantitative spectral analysis of pre-edge peak areas, extracted from bulk X-ray absorption near edge structure (XANES) spectra, determined the average oxidation state of V in the sediment samples to be ∼3.5, indicating a mixture of V(III) and V(IV). Signal-to-noise ratios of XANES spectra were not sufficiently high to allow accurate quantitative analysis by commonly used linear combination fitting approaches. We also demonstrate that high-resolution element mapping by scanning X-ray fluorescence microscopy (SXFM) provides useful complementary geochemical information for resolving possible V host phases in sediments, but is limited in its ability to distinguish V and Ti due to the proximity of their fluorescence emission lines. This study highlights the practical limitations and opportunities of X-ray spectroscopy for investigating V speciation in marine sediments, and reinforces the importance of comprehensively evaluating X-ray spectroscopic techniques prior to applying them to investigating new elements or sample types.

Graphical abstract: Synchrotron X-ray spectroscopy for investigating vanadium speciation in marine sediment: limitations and opportunities

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Supplementary files

Article information


Submitted
11 Jul 2018
Accepted
13 Aug 2018
First published
13 Aug 2018

J. Anal. At. Spectrom., 2018,33, 1689-1699
Article type
Paper

Synchrotron X-ray spectroscopy for investigating vanadium speciation in marine sediment: limitations and opportunities

W. W. Bennett, E. Lombi, E. D. Burton, S. G. Johnston, P. Kappen, D. L. Howard and D. E. Canfield, J. Anal. At. Spectrom., 2018, 33, 1689
DOI: 10.1039/C8JA00231B

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