Analytical pyrolysis and thermal analysis to chemically characterise bitumen from Italian geological deposits and Neolithic stone tools

The chemical study of bitumen from stone tools from Italian Neolithic sites was carried out using analytical pyrolysis-based techniques, EGA-MS (evolved gas analysis mass spectrometry) and DSPy-GC/MS (double shot pyrolysis-gas chromatography/mass spectrometry). The study was mainly aimed at demonstrating the suitability of analytical pyrolysis for studying archaeological bitumen and for obtaining information regarding its origin. EGA-MS was employed to obtain information on the thermal complexity, that is the set of thermal properties and behaviours, of the samples and on their thermal degradation areas and DSPy-GC/MS along with Principal Component Analysis (PCA) were tested for biomarker analysis to assess bitumen source in archaeological objects. Geological bituminous rocks from Central-Southern Italy were selected and used as reference materials to both optimize experimental parameters and to support data interpretation for archaeological samples. Geological samples were also preliminary characterised by thermogravimetric analysis coupled with FTIR spectroscopy (TG-FTIR) under nitrogen and by TG analysis under oxygen to quantify their relative content of organic and inorganic species. The combination of thermal analysis and analytical pyrolysis-based techniques allowed us to quantify the organic content of the bitumen samples and to obtain information on both soluble and insoluble organic fractions. In addition, the proposed approach highlighted the main degradative patterns and the main differences among samples coming from different geographical areas as well as differences between geological and archaeological bitumen. Finally, DSPy-GC/MS associated with PCA proved to be successful in assessing the bitumen source in archaeological objects by the detection of terpanes, distinctive biomarkers.