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Quantifying micro-niche behaviour in sediments: Precise and accurate measurements of DGT gels by laser ablation high resolution laser ablation ICPMS
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
2006 (English)Conference paper, Meeting abstract (Refereed)
Abstract [en]

New developments in micron-scale measurements of trace metals and sulphur contents within sediments by DGT (diffusive gradients in thin-films) have revealed micro-niche structures. The origin of micro-niches is unclear and it is important to understand the relative roles played by inorganic and biological processes in the localised remobilisation of metals. We have undertaken a S and Fe isotope study of micro-niches, to better understand their mechanisms of formation. With their inbuilt pre-concentration, element selection and simple matrix, DGTs are an ideal medium for laser ablation ICPMS. In contrast to analysis of mineral phases, fully matrix-matched standards can be easily made. We have initially concentrated on the measurement of S isotopes and will also present experiments where Fe isotopes have been measured in DGT gels. S and Fe isotopes were measured on a Neptune at mass resolutions of >9000. A New-Wave UP-213 nm laser was used with Ar as the carrier gas. Instrumental mass bias (IMB) for S was corrected for using sample-standard bracketing. Ablation experiments on two S DGT gel standards, 10 Hz, 40% power, 170 μm wide line, scan speed 70 μms-1, show in-run δ34S precisions for DGT gels with 2.1 μmol/cm2 S (3 V of 32S) of <0.2‰ (2SE). There is no observed correlation between δ34S and 32S intensity. Reproducibility on δ34S for individual analytical sessions (4-8 standards) is better than 0.3‰ while the reproducibility over 4 sessions is 0.19‰. Further tests to mimic ablation over micro-niches (continuous ablation across a gel with two isotopic compositions) show similar internal precisions and only slightly worse reproducibility-0.48‰ (2SD; n = 6). The accuracy of the LA δ34S measurements on a BaSO4 gel relative to the reference value of the starting BaSO4, bracketed by a AgI gel of known isotopic composition, is better than 1‰, showing negligible S isotopic fractionation during gel deployment. δ34S variations in micro-niches can be easily resolved at the 1‰ level and 100 μm scale whereas variations in natural micro-niches are expected to be 10‰ or more. Fe measurements, using external normalisation to a 60Ni/61Ni ratio and an exponential law to correct for IMB, suggest internal precisions and external reproducibility of <0.15‰ (2SE) and 0.07‰ (2SD) should be possible.

Place, publisher, year, edition, pages
2006. Vol. 70, A478- p.
Research subject
Applied Geology
URN: urn:nbn:se:ltu:diva-29680DOI: 10.1016/j.gca.2006.06.1418Local ID: 33a79e10-d947-11db-a1bf-000ea68e967bOAI: diva2:1002905
Annual V.M. Goldschmidt Conference : 27/08/2006 - 01/09/2006
Godkänd; 2006; 20120912 (ysko)Available from: 2016-09-30 Created: 2016-09-30Bibliographically approved

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