Abstract
ABSTRACT Archaeological bone collagen is highly useful for radiocarbon (14C) dating and palaeodietary reconstruction. However, collagen preservation and carbon contamination are essential considerations when extracting collagen, becoming especially crucial close to the limit of the method (50,000 years before present = BP). Strong progress has been achieved in the past two decades by 14C and stable isotopic laboratories in removing contamination from archaeological bones, but different pretreatment protocols have been proven to produce varying results. Here we compare three collagen extraction protocols used for palaeodietary studies and 14C dating, considering collagen yield, elemental and stable isotopic data, FTIR analysis, and 14C dates. We focus on the impact of ultrafiltration on the yield and quality of the extracted material. The results again underline the importance of rigorous decontamination methods to gain accurate 14C dates and demonstrate that different protocols have significant effects on the quality and yield of extracted collagen.
Highlights
Collagen extracted from archaeological bones and teeth is one of the most important biomolecules for radiocarbon (14C) dating and palaeodietary studies
3.1.1 Collagen yield The amount of collagen retrieved was lower using Method 1 compared to Method 2
The differences in collagen yield may be related to several factors, which differ between the two methods: 1) Inclusion of the NaOH/HCl step in Method 2 2) Difference in duration and temperature of gelatinisation stage 3) Different brands/cleaning protocols of ultrafilters between the methods
Summary
Collagen extracted from archaeological bones and teeth is one of the most important biomolecules for radiocarbon (14C) dating and palaeodietary studies. A key concern of laboratories specialising in 14C dating or palaeodietary analysis of archaeological bone is the refinement of methods to extract and purify collagen for analysis. This is hampered by three key issues: 1) The degradation of collagen through the rapid or gradual breakup of the peptide chains. 3) less detrimental to 14C dating efforts, endogenous material (such as bone lipids) which are not removed from collagen extracts can significantly alter stable isotopic values and affect palaeodietary interpretations (Liden, Takahashi, and Nelson 1995; Jørkov, Heinemeier, and Lynnerup 2007) Contaminants may derive from the burial environment (such as humic acids or bacteria from the soil), during post-excavation handling and storage (including the application of conservatives) or the laboratory pretreatment and measurement (Nielsen-Marsh and Hedges 2000; Higham 2011). 3) less detrimental to 14C dating efforts, endogenous material (such as bone lipids) which are not removed from collagen extracts can significantly alter stable isotopic values and affect palaeodietary interpretations (Liden, Takahashi, and Nelson 1995; Jørkov, Heinemeier, and Lynnerup 2007)
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