Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size

Authors

  • Felicitas B. Wiedemann-Bidlack,

    Corresponding author
    1. Department of Anthropology, The George Washington University, 2110 G St NW, Washington DC 20009, USA
    Current affiliation:
    1. Department of Biomineralization, The Forsyth Institute, Boston MA 02115, USA.
    • Department of Biomineralization, The Forsyth Institute, Boston MA 02115, USA.
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  • Albert S. Colman,

    1. Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA
    Current affiliation:
    1. Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
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  • Marilyn L. Fogel

    1. Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA
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Abstract

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology-based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.

We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag3PO4 crystals by using a strongly buffered, moderate-temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as δ18O, V-SMOW scale) is typically 0.2–0.3‰ (1 s.d.) on samples as small as 300 µg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen. Copyright © 2008 John Wiley & Sons, Ltd.

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