Bio apatite

Description

“Apatite”, or more precisely the calcium phosphate hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), is the mineral component of enamel, dentine as well as bone and provides the compressive strength of these hard tissues. From a mineralogial point of view, it corresponds more to a carbonate apatite (dahllite). It should rather be referred to as “biological apatite” or “bioapatite” because it contains structural carbonate and numerous substitutions of minerals and trace elements. Enamel consists of approx. 96% of bioapatite and dentine or bone of approx. 70% of this mineral component.

The substitution of the main element calcium by the trace element strontium is of central importance for bioarchaeometric analyses. The incorporation of strontium into the crystal structure is due to the similar properties of both elements, so that 99% of the strontium contained in the body of mammals is stored in bones and teeth. Strontium isotope analysis for the investigation of mobility is therefore usually carried out on the mineral component of teeth or bones.

Oxygen isotope analysis to reconstruct mobility, but also to study seasonality and climate-related issues, can be performed both for the oxygen bound in the PO₄^3- group and for the oxygen bound in the structural carbonate (CO₃^2-). The latter can replace the OH^– or PO₄^3- groups in bioapatite.

The structural carbonate of bioapatite also offers the possibility to perform carbon isotope analysis for dietary reconstruction. In contrast to the carbon contained in collagen, which mainly originates from proteins, the carbon of the structural carbonate reflects a cross-section of the total diet.

Sample properties

Depending on the type of analysis, at CEZA bioapatite samples of enamel or bone are separated from teeth or larger bones and usually pre-treated with weak acetic acid against minerals of diagenetic origin. By prior arrangement, we may also analyze externally prepared samples.

We recommend the following minimum sample quantities:

Strontium isotope analyses

• 5 mg of pre-treated enamel or bone powder for subsequent separation of Sr under clean room conditions

Oxygen isotope analyses (PO₄^3-)

• 10 – 12 mg of homogenized enamel or bone powder for subsequent pre-treatment and silver phosphate precipitation

Oxygen isotope analyses (CO₃^2-)

• A few milligrams of homogenized and, if necessary, pre-treated enamel or bone powder for subsequent weighing and analysis or
• 10 – 12 mg of homogenised enamel or bone powder for samples to be pre-treated at CEZA