Kerwin J L, Wiens A M, Ericsson L H
Department of Botany, University of Washington, Seattle 98195, USA.
J Mass Spectrom. 1996 Feb;31(2):184-92. doi: 10.1002/(SICI)1096-9888(199602)31:2<184::AID-JMS283>3.0.CO;2-2.
Low-energy negative-ion electrospray mass spectrometry (ESI-MS) and ESI-MS/MS were used to characterize saturated and unsaturated fatty acids. The carbon number and degree of unsaturation of fatty acids were determined using ESI-MS, and MS/MS was used to localize some double bond positions of mono-and polyunsaturated fatty acids. For compounds with up to two unsaturated bonds, fragmentation was dominated by loss of H2O from the carboxyl moiety and very low-intensity peaks generated from bonds cleaved at carbons alpha and/or beta to sites of unsaturation. Fragmentation of monounsaturated fatty acids was minimal using this soft method of mass spectrometric analysis, but increased with progressively greater degrees of fatty acid unsaturation. There was extensive hydride migration during ESI-MS/MS of compounds with three or more double bonds. Although this behavior complicated localization of double and triple bonds, the spectra were reproducible. Many peaks could not be definitively assigned to specific product ions, but the spectra of standards and complementary natural products were similar and isobaric compounds could be differentiated. The utility of this technique to examine biological samples was shown by analysis of the fatty acid composition of cod liver oil. Detection limits for negative-ion ESI-MS/MS were at or below 1 pg.
低能量负离子电喷雾质谱（ESI-MS）和ESI-MS/MS被用于表征饱和脂肪酸和不饱和脂肪酸。脂肪酸的碳原子数和不饱和度通过ESI-MS测定，而MS/MS则用于确定单不饱和脂肪酸和多不饱和脂肪酸的一些双键位置。对于含有至多两个不饱和键的化合物，碎片化主要是由于羧基部分失去H2O，以及在不饱和位点的α和/或β碳原子处断裂的键产生的极低强度峰。使用这种软质质谱分析方法，单不饱和脂肪酸的碎片化程度最小，但随着脂肪酸不饱和度的逐渐增加而增加。在具有三个或更多双键的化合物的ESI-MS/MS过程中存在广泛的氢化物迁移。尽管这种行为使双键和三键的定位变得复杂，但光谱是可重复的。许多峰无法明确归属为特定的产物离子，但标准品和互补天然产物的光谱相似，且等压化合物可以区分。通过分析鳕鱼肝油的脂肪酸组成，展示了该技术用于检测生物样品的实用性。负离子ESI-MS/MS的检测限为1 pg或更低。
