Figure 2.

(a) Partial high-temperature gas chromatograms showing total lipid extracts from three sherds above mass chromatograms from aliquots analysed using GC/MS operated in SIM mode for the detection of (b) C₁₈–C₂₂ DHYAs (as tris-trimethylsilyl derivatives) and (c) C₁₈–C₂₂ APAAs (as methyl esters; electronic supplementary material, tables S1 and S2). Components were identified based upon the presence of identical chromatographic peaks for the characteristic fragment ions and molecular ions at the expected retention times. Residue (i) is from the Neolithic settlement at Braes o'Habreck on Wyre, the Orkney Isles; (ii) is from Cille Pheadair, South Uist; and (iii) is from Jarlshof, Shetland; only (ii) and (iii) contain detectable marine biomarkers, with (iii) displaying the strongest signatures. Filled circles represent free fatty acids with carbon number x and degree of unsaturation y. Retention window: (a) 5–35 min, (b) 23–30 min and (c) 24–36 min.