Assessing a modified carbonate digestion protocol for increased carbon dioxide recovery during cremated bone pretreatment

Giannì, Maddalena ORCID: https://orcid.org/0000-0002-8099-3553, Griffiths, Seren ORCID: https://orcid.org/0000-0001-5168-9897, Wood, Rachel ORCID: https://orcid.org/0000-0002-1694-3295 and Chivall, David (2024) Assessing a modified carbonate digestion protocol for increased carbon dioxide recovery during cremated bone pretreatment. Radiocarbon, 66 (5). pp. 1109-1119. ISSN 0033-8222

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Abstract

Cremated bones are a commonly preserved material and often found in burial environments where unburned bone may not be preserved. As such direct radiocarbon dating of cremated bone could be essential in determining the chronology of an event. Pretreatment of cremated bone exploits the structural carbonate component of the bone which survives cremation. However, due to the low abundance (ca. 0.1%) of this component, the extraction of an amount of endogenous carbon sufficient for radiocarbon dating may represent a challenge. Here we investigate two modifications to the phosphoric acid digestion protocol used during the preparation of cremated bones at the Oxford Radiocarbon Accelerator Unit (ORAU). The first of these was to use ultrasonication to release evolved CO2 from the viscous phosphoric acid and cremated bone mixture that is formed during digestion. The second was to double the amount of time during which evolved CO2 was removed from the reaction vessel by transfer into a cryogenically cooled ampoule. Ultrasonication of the digestion mixture failed to produce a significantly higher carbon yield, while double-time collection resulted in an average 21.5±13.8% increase of C yield without affecting the measured age. Extending the collection time can better enable reliable dating of small (less than 1 g) samples.