Evaluation of possible contamination sources in the C-14 analysis of bone samples by FTIR spectroscopy

In the sample preparation laboratory of CEDAD (CEnter for DAting and Diagnostics) of the University of Lecce, a protocol for the quality control of bone samples based on infrared spectroscopy has been set up. The protocol has been recently developed as a check-in test with the aim to identify the presence of collagen in the samples, assess its preservation status, and determine whether the submitted bone samples are suitable for accelerator mass spectrometry (AMS) radiocarbon measurements or not. We discuss in this paper the use of infrared-based techniques to identify the presence of contaminants such as restoration and consolidation materials, humic acids, and soil carbonates, which, if not removed by the sample processing chemistry, can be sources of exogenous carbon and can thus influence the accuracy of the C-14 determinations. Bone samples recovered in well-defined and previously dated archaeological contexts were intentionally contaminated, submitted to the standard method for collagen extraction and purification, and then characterized by means of Fourier transform infrared (FTIR) spectroscopy analyses performed in attenuated total reflection (ATR) mode before being combusted, converted to graphite, and measured by AMS. The study shows that the ATR-FTIR technique is an extremely powerful method for the identification of both the collagen and its contaminants and can supply important information during the selection and processing of samples to be submitted for C-14 dating.