Optimizing FTIR method for characterizing diagenetic alteration of skeletal material

Abstract

Diagenetic alterations may limit the potential use of archaeological bones and teeth as a reliable source of information about the origin and movement of people and animals, their diet and the environment in which they lived. Fourier transform infrared spectroscopy (FTIR) has been widely applied to determine the overall state of preservation of ancient bones. Spectral data are commonly used to quantify two diagenetic indicators related to sample crystallinity: the splitting factor (SF), the hydrogen phosphate ion index (HPO4/PO4) and the width at 85% of the height of the 604 cm-1 peak (FW85%).The aim of the present work is to determine the presence of any difference in the value of SF, HPO4/PO4 and FW85% of the 604 cm−1 peak between tissues such as enamel, dentine and bone. This method has been applied to two different modern animals: sheep and pigs.The results obtained in this study demonstrate that enamel has significantly higher values of the SF and significantly lower values of HPO4/PO4 and FW85% in comparison to bone and dentine in both animal species. Moreover, enamel has been reported to show diversification of SF index across the investigated species, which is presumably related to different tooth development and mineralisation patterns in animals with different diets (i.e. herbivorous versus omnivorous). The present study demonstrates that due to the different biogenic chemical structure of bones and teeth, the SF and HPO4/PO4 reference ranges should be determined separately for each of the three tissues, and in the case of enamel also allowing for the analysed species.