Gas chromatographic mass spectrometric detection of dihydroxy fatty acids preserved in the 'bound' phase of organic residues of archaeological pottery vessels.

A methodology is presented for the determination of dihydroxy fatty acids preserved in the 'bound' phase of organic residues preserved in archaeological potsherds. The method comprises saponification, esterification, silica gel column chromatographic fractionation, and analysis by gas chromatography/mass spectrometry. The electron ionisation mass spectra of the trimethylsilyl ether methyl ester derivatives are characterised by fragment ions arising from cleavage of the bond between the two vicinal trimethylsiloxy groups. Other significant fragment ions are [M-15](+.), [M-31](+.), m/z 147 and ions characteristic of vicinal disubstituted (trimethylsiloxy) TMSO- groups (Δ(7,8), Δ(9,10), Δ(11,12) and Δ(13,14): m/z 304, 332, 360 and 388, respectively). The dihydroxy fatty acids identified in archaeological extracts exhibited carbon numbers ranging from C(16) to C(22) and concentrations varying from 0.05 to 14.05 µg g(-1) . The wide range of dihydroxy fatty acids observed indicates that this approach may be applied confidently in screening archaeological potsherds for the degradation products of monounsaturated fatty acids derived from commodities processed in archaeological pottery vessels.