Chemical profile of organic residues from ancient amphoras found in Pyrgi and Castrum Novum, Tyrrhenian Sea (Italy)

Abstract

The organic residues in the form of black layer spots inside amphoras found on the sites of the former ancient ports of Pyrgi and Castrum Novum on the coast of the Tyrrhenian Sea were investigated using GC–MS and HPLC with fluorimetric detection. According to our hypothesis, the residues could be from waterproofing materials from pine trees, which ensured that amphoras could be used for transportation and the storage of liquids. Samples of the residues were removed, extracted with hexane and separated into three parts. The first part served directly for GC–MS analysis of hydrocarbons. The second part after the evaporation of hexane and silylation of the residue with MSTFA was used for the analysis of fatty and resin acids. Finally, the third part after evaporation of hexane and dilution of the residue with methanol was used for HPLC analysis of pinosylvin mono methyl ether and confirmation of retene presence using a fluorimetric detector. 18-Norabieta-8,11,13-triene, 19-norabieta-8,11,13-triene and 1,2,3,4-tetrahydroretene were found in the hexane extract, which are intermediates from the tar/pitch production process. The most abundant peak in the chromatogram of the hexane extract was dehydroabietic acid and retene. The latter is considered to be a marker for pine pitch. The most abundant compound in the derivatized hexane extract was also dehydroabietic acid, which occurs only as a minor component in fresh resins. This molecule is formed during the oxidative dehydrogenation of abietic acid, which predominates in original resins. Pinosylvin mono methyl ether was found in the methanolic extract using HPLC with fluorimetric detection and, to the best of our knowledge, it is the first finding of this substance in archaeological samples. Together with the abovementioned compounds, it supports the hypothesis of the resin's origin from trees of the Pinaceae family.