Molecular archaeology: Analysis of charred (food) remains from prehistoric pottery by pyrolysis—gas chromatography/mass spectrometry

Abstract

The suitability of analytical pyrolysis techniques for the chemical characterisation of amorphous (charred) organic residues obtained from prehistoric pottery was studied. No chemical preparation of the sample was needed and the analysis was performed on very small samples (20–30 μg). Curie-point pyrolysis mass spectrometry and Curie-point pyrolysis gas chromatography were used for rapid characterisation of 33 residue-samples obtained from the outside (5) and inside (28) of different types of pottery from the native Roman settlement at Uitgeest-Groot Dorregeest (Netherlands). Discriminant analysis of the data shows several groups of residues of different chemical composition. Four representative residue samples were selected for more detailed analysis by Curie-point pyrolysis—gas chromatography/mass spectrometry. Many bio-organic moieties were detected in the residues situated on the inside of pots including fatty acids and characteristic markers for proteins and polysaccharides. Since no indications could be found to assume severe post-depositional changes in chemical composition, it is clear that the composition of the residues is a reflection of the original use in prehistoric times. The refractory nature of the charred (food) residues causes the preservation of the bio-organic characteristics. Other classes of compounds, such as polycyclic aromatic hydrocarbons, were detected in residues from the outside and were interpreted as smoke condensates from open cooking fires. A regular alkane/alkene pattern found in many residues and in the ceramic material of the pot sherd is interpreted as the pyrolysis product of an aliphatic network that has been formed from foodstuffs under high temperature conditions during cooking.