A complementary approach using analytical pyrolysis to evaluate collagen degradation and mineral fossilisation in archaeological bones: The case study of Vicenne-Campochiaro necropolis (Italy)

Spectroscopic (FTIR), diffractometric (XRD), thermogravimetric (TGA) analyses were applied along with off-line analytical pyrolysis combined with GC–MS (Py/GC–MS) in order to understand the relationships between mineral composition, degree of crystallinity of carbonated hydroxylapatite (cHA), organic content and the occurrence of collagen content in archaeological bones subjected to diagenesis. Osteological samples came from Vicenne-Campochiaro necropolis in Molise (Italy). Bones mineral composition was investigated by XRD while cHA crystallinity was assessed by the crystallinity index (CI) obtained from diffractometric analysis and the Infrared Splitting Factor (IRSF) obtained from FTIR spectra. The organic fraction of the archaeological bones was quantified by TGA and characterised by Py/GC–MS. The quantity of 2,5-diketopiperazines (DKPs) produced upon pyrolysis was used as a parameter to assess quantities of collagen inside each specimen. Attention was paid to proline (Pro) and hydroxyproline (Hyp) containing DKPs, in particular cyclo(Hyp–Pro), recognised to be specific marker of collagen pyrolysis. The relative distributions of DKPs in the pyrolysates of archaeological samples and fresh bovine bone sample were rather similar suggesting good preservation of the collagen and non-collagenous proteins in all the ancient osteological tissues. The absolute quantity of DKPs in the bone samples were different and in good accordance with the total organic matter detected by TGA and consistent with cHA high degree of crystallinity and FTIR data.