Determination of collagen by pyrolysis/GC-MS. Evaluation of
the degree of conservation of archeological bones from
Vicenne (Italy) by comparison with XRD, TGA and FTIR
analysis
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Abstract
Human bones and teeth are frequently recovered at archaeological sites. Their state
of preservation may depend on the mode and the burial environment. The content
of collagen and the degree of crystallinity of carbonate hydroxyapatite (HA) are
among the indicators adopted to evaluate the conservation status of bones.
Analytical pyrolysis (Py) [1] together with X-ray powder diffraction (XRD),
Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis
(TGA), were used at this scope. In this work, a new quantitative procedure in Py
was employed to characterise residual proteins in five bone samples from the
medieval necropolis of Vicenne-Campochiaro (Molise, Italy)[2].
The yields of cyclic dipeptides (2,5-diketopiperazines, DKPs) evolved form the
pyrolysis of the samples, including the cyclo(proline-hydoxyproline) as distinctive
marker of collagen, were determined by GC-MS with and without silylation. The
detection of DKPs enabled the identification of collagen in all the analysed
samples, in accordance to the FTIR spectra showing the characteristic amide peak.
The presence of organic matter along with that of carbonatic phases was confirmed
and estimated by TGA. XRD data showed that the samples mainly contained HA
having different degrees of crystallinity; small amounts of quartz and calcite were
also detected in some samples. The quantitative experimental data were combined
to provide a relative estimate of the degree of conservation of the bone samples.
The bones of an adult young female (t.139) and an aged male (t.165) resulted to be
the worst and best preserved, respectively. The tombs were located in the same area
where the acidity of the soil has damaged nearly all the skeletons. The skeleton
from t.165 was almost complete, whereas the one from t.139 was lacking in many
bones. Therefore biological (age-at-death, sex) and ritual (care, depth) factors as
well as specific conditions of each burial could be involved in the observed
different preservation state