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| Titel |
Least destructive sampling of human remains using laser drilling for Sr isotope analysis by TIMS |
| VerfasserIn |
Malte Willmes, Ian Moffat, Rainer Grün, Richard Armstrong, Les Kinsley, Linda McMorrow |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077717
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| Zusammenfassung |
| Strontium isotope ratios (87Sr/86Sr) measured in ancient human remains can be used to
reconstruct migration patterns of ancient human populations. This application is based on the
fact that different geologic regions have distinct Sr isotope signatures that are cycled through
the soils, plants and rivers, and eventually enter the food cycle. Sr isotope ratios measured in
skeletal remains (bones and teeth) reflect the average of dietary Sr that was consumed when
the tissue was formed, allowing the investigation of human migration between geologically
distinct terrains.
The analysis of human remains is always a sensitive topic requiring minimal damage to
the sample, while at the same time providing highly precise and accurate results. Samples can
be analysed either by solution methods like thermal ionisation mass spectrometry (TIMS), or
by in-situ laser ablation MC-ICP-MS.
For TIMS a drill is used to extract a small amount of sample, which is then digested in
acid and Sr is separated out using ion exchange chromatography. This technique provides
highly precise and accurate results, because any isobaric interferences are removed during
chemical separation. The drawback is that drilling may cause visible damage to the sample,
restricting access to precious human remains.
LA-MC-ICP-MS analysis is very fast and nearly destruction free. However, the accuracy
and precision of LA-MC-ICP-MS is limited by a number of factors including large
instrumental mass discrimination, laser-induced isotopic and elemental fractionations and
molecular interferences on 87Sr. Its application thus requires rigorous data reduction, which
can introduce significant uncertainties into the analysis. This is especially true for samples
with relatively low Sr concentrations such as human teeth (e.g., Woodhead et al., 2005;
Horstwood et al., 2008; Vroon et al., 2008). In addition, LA-MC-ICP-MS has traditionally
required a flat sample surface, thus an unbroken tooth needs to be cut, which is rather
destructive.
To evaluate sample strategies which cause minimal damage we have used laser drilling to
extract material from the outside of the tooth. Spot sizes between 100-233μm were used to
ablate tooth enamel and collect it in a Teflon beaker. The ablated material was then digested
in acids, underwent chemical separation for Sr, and was measured using TIMS. This method
minimises sample damage, allows for a large sample throughput and at the same time offers
high precision and accuracy. While this method is considerably slower than using
conventional LA-MC-ICP-MS, it circumvents the complicated data reduction and its
associated uncertainties.
Horstwood, M., Evans, J., & Montgomery, J. (2008). Determination of Sr isotopes in
calcium phosphates using laser ablation inductively coupled plasma mass spectrometry and
their application to archaeological tooth enamel. Geochimica et Cosmochimica Acta, 72(23),
5659–5674. doi:10.1016/j.gca.2008.08.016
Vroon, P. Z., van der Wagt, B., Koornneef, J. M., & Davies, G. R. (2008). Problems in
obtaining precise and accurate Sr isotope analysis from geological materials using
laser ablation MC-ICPMS. Analytical and bioanalytical chemistry, 390(2), 465–76.
doi:10.1007/s00216-007-1742-9
Woodhead, J., Swearer, S., Hergt, J., & Maas, R. (2005). In situ Sr-isotope analysis of
carbonates by LA-MC-ICP-MS: interference corrections, high spatial resolution and an
example from otolith studies. Journal of Analytical Atomic Spectrometry, 20(1), 22.
doi:10.1039/b412730g |
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