Gas-liquid chromatography mass spectrometry of the 4,4-dimethyloxazoline derivatives of Delta 5-unsaturated polymethylene-interrupted fatty acids from conifer seed oils

The fatty acids from the seed oils of three Conifer species lone Pinaceae, Pinus pinaster, and two Cupressaceae, Chamaecyparis lawsoniana and Biota orientalis) have been analyzed as their 4,4-dimethyloxazoline (DMOX) derivatives by gas-liquid chromatography coupled with mass spectrometry. The structures of six Delta 5-unsaturated polymethylene-interrupted fatty acids (Delta 5-UPIFA) were established, confirming previous studies in which they were identified by their equivalent chain-lengths (ECL) and by comparison with related authentic standards. These acids were: cis-5,cis-9 18:2, cis-5,cis-9,cis-12 18:3 (P. pinaster), cis-5,cis-9,cis-12,cis-15 18:4 (C. lawsoniana), cis-5,cis-11 20:2, cis-5,cis-11,cis-14 20:3 (all species), cis-5,cis-11,cis-14,cis-17 20:4 (B. orientalis) acids. In addition, cis-9 18:1, cis-9,cis-12 18:2 (all species) and cis-9,cis-12,cis-15 18:3 (Cupressaceae) acids, together with their elongation products [cis-11 20:1, cis-11,cis-14 20:2 (all species) and cis-11,cis-14,cis-17 20:3 (B. orientalis) acids] were also identified. In the mass spectra, DMOX derivatives of all Delta 5-UPIFA showed an intense peak at m/z 153, which is a diagnostic ion of fatty acid derivatives with a Delta 5-ethylenic bond. Other double bonds were localized by ion pairs that differed by 12 atomic mass units. The present study fully justifies the use of ECL to identify Delta 5-UPIFA in Conifer seed oils, in which they are ordinary components.