Study of organic residues

The Fourier-transform infrared spectroscopy (IRTF), used in ATR mode or microscopy, is an essential analytical technique for identifying major families of organic compounds in archaeological materialsThis method allows for the detection of lipids, waxes, natural resins, or proteins from their characteristic spectral signatures.

However, the presence of mineral matter can generate spectral interferences, making the identification of organic compounds more delicate. To overcome this limitation, FTIR is generally employed as a preliminary technique. CIRAM specialists integrate it into multi-technique analytical protocols, in association with chromatography or Raman spectroscopy, in order to refine the identification of organic residues.

Gas chromatography-mass spectrometry (GC-MS) is a reference technique for the analysis of organic compounds in archaeology. This technique relies on the separation of molecules present in a sample using gas chromatography (GC), followed by precise identification of the constituents by mass spectrometry (MS), based on their mass-to-charge ratio.

This method enables trace compounds to be detected and quantified, providing essential information on their chemical composition.

Thanks to it, CIRAM experts identify specific biomarkers, allowing them to reconstruct the nature of ancient substances such as vegetable oils, animal fats, tannins, or tars. This expertise contributes to the interpretation of the cultural and economic practices of ancient societies, by revealing the uses and transformations of organic materials over time.

Primarily used for the analysis of mineral materials, Raman spectrometry nevertheless constitutes a valuable complementary technique in archaeometry. Its main advantage lies in its non-destructive nature, allowing samples to be studied without alteration or prior preparation.

Thanks to excellent spatial resolution, this method allows the analysis of organic residues at the microscopic scale (on the order of a few microns). CIRAM researchers integrate Raman spectrometry into multimodal analysis protocols, coupling it with FTIR spectroscopy and GC-MS chromatography. This combined approach is essential for the characterization of complex substances and allows for the precise identification of organic materials used by past societies.

Carpology is the study of seed and fruit remains from archaeological contexts such as vessels or sediments. The analysis of these plant macro-remains provides valuable insights into the agriculture, diet, and exploitation of plant resources by ancient societies. Even when carbonized, these seeds can be identified by CIRAM scientists to reconstruct past environments.

The palynology, centered on the study of pollen and spores, complements carpology and anthracology (study of charcoal) in the reconstruction of ancient landscapes and climates. The analyses carried out by CIRAM, via optical and electron microscopy, allow for the identification of pollen grains according to their morphology and structure, thus refining paleoenvironmental models and territorial occupation dynamics.