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Methodological considerations for the use of acid based pre-treatment protocols for carbon and oxygen analysis of tooth enamel
  • Varkuleviciute Karolina,
  • Winter-Schuh Christine,
  • Cheryl Makarewicz
Varkuleviciute Karolina
Christian Albrechts Universitat zu Kiel Institut fur Ur- und Fruhgeschichte
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Winter-Schuh Christine
Christian Albrechts Universitat zu Kiel Institut fur Ur- und Fruhgeschichte
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Cheryl Makarewicz
Christian Albrechts Universitat zu Kiel Institut fur Ur- und Fruhgeschichte

Corresponding Author:[email protected]

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Abstract

Rationale: Chemical pre-treatment is an important methodological step aimed to remove exogenous materials introduced to archaeological tooth enamel through various diagenetic pathways prior to carbon and oxygen isotope analysis. Concerningly, some of these pre-treatment methods (NaClO, H 2O 2 and CH 3COOH) have been shown to cause significant changes to enamel chemical properties and stable isotope values. This study aims to re-examine the effects of commonly used pre-treatment protocols applied to the enamel structure on bioapatite δ 13C and δ 18O values, as well as investigate patterns related to site burial context and sample preservation, as indicated by pre-screening using Fourier Transform Infrared (FTIR) spectroscopy. Methods: Modern and archaeological samples were subjected to ten commonly used pre-treatment protocols using NaClO, H 2O 2 and CH 3COOH at various time intervals. Preservation status and diagenetic alteration prior to and after treatment were investigated using Attenuated Total Reflectance- Fourier Transform Infrared Spectroscopy (ATR-FTIR). δ 13C and δ 18O values were measured before and after the treatment to determine if treatments induced isotopic shifts. Results: The results show that all pre-treatment protocols caused shifts in δ 13C and δ 18O values in the range of 0‰ to ±1.5‰ in both archaeological and modern samples. Most treated samples also shown increased crystallinity, likely indicating sample recrystallisation. We argue that these changes are indicative of more than just removal of contamination and diagenetic alterations, but also of dissolution and/or restructuring of the enamel carbonate leading to changes to the in vivo isotope signal. Conclusions: We recommend careful consideration of sample burial context and possible routes of diagenesis when choosing a pre-treatment protocol. Use of H 2O 2 and NaClO to remove organic matter from samples is discouraged as it incurs unwanted changes to the enamel chemical properties and isotope values. We also recommend use of only short acetic acid treatment protocols to avoid possible recrystallisation during prolonged contact.
12 Aug 2024Submitted to Rapid Communications in Mass Spectrometry
12 Aug 2024Submission Checks Completed
12 Aug 2024Assigned to Editor
12 Aug 2024Review(s) Completed, Editorial Evaluation Pending
06 Sep 2024Reviewer(s) Assigned
17 Oct 2024Editorial Decision: Revise Major