Studies of structure and mechanism in acetonitrile chemical ionization tandem mass spectrometry of polyunsaturated fatty acid methyl esters

摘要: Recently it has been shown that acetonitrile chemical ionization tandem mass spectrometry (CI-MS/MS) is a rapid, on-line means to determine double bond position in fatty acid methyl esters (FAME). The mechanism of this gas phase condensation reaction studied. Evidence the (1-methyleneimino)-1-ethenylium ion (m/z 54), formed upon with itself, adding across [2+2] cycloaddition observed. When nascent complex undergoes collision-induced dissociation, two diagnostic ions emerge. One these results from loss hydrocarbon end FAME, whereas other ester end, and when considered together, localize positions bonds FAME. Several labeling MS/MS/MS experiments on were performed plausible fragmentation stable (1-methyleneimino)-1-ethenylium—FAME complex. first generation product ions, or appear be though charge-driven mechanism, second are via charge-remote fragmentations. Plausible mechanisms for formation subsequent dissociation presented monounsaturated, diunsaturated, polyunsaturated (3 more bonds)