Method: Biogenic Apatite (CaPO₄) Isotope Analysis

Pretreatment

Samples are sectioned to target the desired bone/tooth substructure before being ultrasonicated to remove any debris (and if necessary placed through additional cleaning to remove contaminating carbonates). The samples are then pulverized with a mortar and pestle and put through a rigorous oxidative cleaning. First they are immersed in Sodium hypochlorite (NaOCl) for 24 hours to oxidize any organic material, and then in sodium hydroxide (NaOH) for a further 24 hours to remove and humic substances. After thorough rinsing the sample is then dissolved in hydrofluoric acid (HF), and collected to separate it from the CaF2 precipitate. This dissolved sample is then titrated with a silver amine solution, and heated leading to the evaporation of volatile compounds and the formation of a crystal lattice of Ag₃PO₄. This lattice is then put through multiple rounds of rinsing/centrifuging before being dried and weighed.

Isotope Measurement

Prepared samples are packaged in silver foil alongside a full methodological standard and then measured on the Thermo Scientific high temperature conversion elemental analyzer with zero-blank autosampler coupled with an isotope ratio mass spectrometer (TC/EA-IRMS) for isotopic analysis. Each sample is run in triplicate.

Results

Phosphate results are reported as δ¹⁸O corrected to VSMOW using a three standard regression. Uncertainties for each sample measurement is presented as the 95% confidence interval (CI).