Impact of contamination and pre-treatment on stable carbon and nitrogen isotopic composition of charred plant remains.
Bottom Line: Pre-treatment protocols have been adapted in distinct forms from radiocarbon dating, but insufficient research has been carried out on evaluating their effectiveness and necessity for stable carbon and nitrogen isotope analysis.The results show a ca 1‰ decrease in the δ(15)N values of archaeological charred plant material caused by harsh acid treatments and ultra-sonication.This study fills an important gap in plant stable isotope research that will enable future researchers to evaluate potential sources of isotopic change and pre-treat their samples with methods that have been demonstrated to be effective.
Affiliation: Research Laboratory for Archaeology and the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, UK.Show MeSH
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Mentions: Figure6(a) shows the IR spectra of the humic salt, the humic contaminated samples and the uncontaminated sample. The spectra of the archaeological samples and the pure humic salt are extremely similar, except for two regions, which produce higher peaks at 10% and 50% contamination (peaks at 1010, 1080 and 3690 cm–1). The undetectable 5% humic acid contamination does not significantly alter the δ13C and δ15N values of the sample (–23.2‰ and 6.2‰, respectively; compared with the uncontaminated δ13C value of –22.9‰ and δ15N value of 6.4‰). The presence of 10% and 50% contamination causes larger shifts in the δ13C values (–23.6‰ and –24.4‰, respectively) than in the δ15N values (5.9‰ and 5.6‰), which is not unexpected since the humic salt had a significantly higher C/N ratio than the sample (24.3 vs 6.0). It is important to note, however, that large variability exists in the C/N ratios of different humic acids (e.g.) so their impact on the stable isotope composition of contaminated grain may be drastically different.
Affiliation: Research Laboratory for Archaeology and the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, UK.