$^{14}$C dating of molecular biomarkers. Recent developements at LSCE and application to archaeological butters

International audienceEstablishing robust and precise chronological frameworks remains a major challenge for archaeological sciences. During the last decades, the possibility of carrying out $^{14}$C measurements on minute quantities of carbon has extended the spectrum of possibilities. In particular it opens opportunities to determine the age of fossil molecules preserved in various types of archives. However, this method suffers from the absence of standards validated and adopted by the entire community.Within the Paris Saclay Geosciences Analytical Platform (PANOPLY), the LSCE is developing this method and is now able to offer it to the community. As part of a dating intercomparison exercise on specific compounds proposed by the University of Bristol, we determined by EchoMICADAS the age of fatty acids with 16 and 18 carbon atoms present in fossil butters and in a current butter. Fossil butters were provided by the National Museum of Ireland. These are butters preserved in peat bogs and dated, for one, to the Bronze Age and, for the other, to the post-medieval period. The current butter (Elle et Vire, 250 g, without preservatives or additives, 60% fat, produced on 02/11/2022) was acquired in supermarkets.We used the extraction/esterification protocol and purification conditions of individual compounds by preparative gas chromatography (prep-GC) proposed by Casanova et al. (2018). The contribution of the carbon added during the esterification was corrected after determination of the $^{14}$C of the methanol. The $^{14}$C of the raw butter aliquots was determined by Compact Radiocarbon System (ECHoMICADAS) in graphitization mode and that of the compounds by EA-GIS or graphitization. The quantities of extracted/esterified fatty acids were determined during injections in prep-GC. Purification yields are estimated using the amount of carbon in each sample, determined by EA-GIS, converted to mass of esterified fatty acid.The dating results are in agreement with those of Casanova et al. (2021) for fossil butters and with those of Hua et al. (2021) for current butter. The standard deviations are about 100 years for the results acquired by EA-GIS and ~50 years in graphitization mode