An application of high performance liquid chromatography to analysis of lipids in archaeological samples

Five samples from three different types of 1500-year-old Mediterranean amphorae, as well as from a contemporary oil lamp found in the same deposit, were analyzed for the presence of lipid residues. Each sample of finely ground amphorae powder weighed 1-2 g. The abundance of interfering secondary products makes thin-layer chromatography (TLC) an essential step of the procedure. The fractionation of the extract into its various lipid components by means of TLC was followed by quantitative recovery of the triglyceride (TG) and free fatty acid (FFA) fractions from the plates and by the measurement of their components by high performance liquid chromatography (HPLC) after esterification. The minimum detectable level is 1 ng. The amphorae samples revealed a more abundant FFA fraction than a TG fraction, which is the reverse of what we know about the composition of fresh oil. Despite the considerable age of the amphorae and their preservation under non-ideal conditions, the lipid residues have retained certain identifiable characteristics that enable one to make valid suggestions as to the type of commodity originally transported in the amphorae. The results of these experiments yield important information that enables the biochemist to observe an aging process irreproducible in the laboratory and provides the archaeologist with previously unavailable information about trade 15 centuries ago.