Analysis of Linolenic Acid Isomers by Gas Chromatography - Mass Spectrometry
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Abstract:
The elution order of peaks and the mass spectral features of linolenic acid isomers were studied by gas chromatography-mass spectrometry. The results indicated that there were certain patterns in the elution order of peaks of fatty acids using a strong polar capillary column BPX-70 (120 m × 0.25 mm × 0.25 μm). For the analyzed linolenic acid isomers, the elution order of peaks were C18:3 9t,12t,15t; C18:3 9c,12t,15t; C18:3 9t,12c,15t; C18:3 9t,12t,15c; C18:3 9c,12c,15t; C18:3 9c,12t,15c; C18:3 9t,12c,15c; and C18:3 9c,12c,15c. According to the analyses of fragment patterns and mass spectral features, the characteristic ions of ?-linolenic acid methyl ester were m/z 79, 108 (? ion), 236 (? ion), 261, and 292 and those of γ-linolenic acid methyl ester were m/z 79, 150 (? ion), 194 (? ion), 261, and 292. Among the eight cis and trans isomers of ?-linolenic acid, when there was a cis double-bond at the 12 position, the base-peak ion was m/z 79, and was accompanied by an apparent ? ion (m/z 108) and an ? ion (m/z 236). When there was a trans double-bond at the 12 position, the ? ion disappeared, the ? ion intensity was weakened, and the ion intensity of m/z 107 was greater than that of m/z 108. Additionally, when there was a second trans double-bond at the 15 position, the base-peak ion was m/z 95; however, when there was a second cis double-bond at the 15 position, the base-peak ion was m/z 67. The double-bond positions and cis-trans isomers of linolenic acid have significant impacts on mass spectral features, and the cis and trans isomers at the 12 position show greater influences than those at positions 9 or 15.
