Journal of Lipid Research, Vol 19, 172-176, Copyright © 1978 by Lipid Research, Inc.
Determination of double bond positions of unsaturated fatty acids by a chemical ionization mass spectrometry computer system
T Murata, T Ariga and E Araki
After stereospecific oxidation, trimethylsilylated methyl esters of mono-
and diunsaturated fatty acids were analyzed by combined gas- liquid
chromatography-chemical ionization mass spectrometry. The positions of
original double bonds were deduced from the fragment ions produced by the
cleavage of the carbon-carbon bond between two trimethylsilyl ethers. These
fragment ions were recorded at m/e 187 and 259 in the case of 16:1(n-7), at
m/e 187 and 287 in the case of 18:1(n- 7), at m/e 215 and 259 in the case
of 18:1(n-9), and at m/e 172 and 259 in the case of 18:2(n-6),
respectively. The diastereoisomers of monounsaturated fatty acids can be
discriminated by comparing the intensities of the fragment ions at m/e 253
and 285 in the case of 16:1 and at m/e 281 and 313 in the case of 18:1. The
diastereosiomers of diunsaturated fatty acids may also be distinguished
from each other by comparing the intensities of the fragment ions formed by
the loss of trimethylsilyl function from the characteristic ions. Mono- and
diunsaturated fatty acids in liver may be dominantly in cis- 18:1(n-1) and
cis-cis-18:2(n-6) as determined by a mass chromatographic technique.
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