Abstract
Double and triple bonds have significant effects on the biological activities of lipids. Determining multiple bond positions in their molecules by mass spectrometry usually requires chemical derivatization. This work presents an HPLC/MS method for pinpointing the double and triple bonds in fatty acids. Fatty acid methyl esters were separated by reversed-phase HPLC with an acetonitrile mobile phase. In the APCI source, acetonitrile formed reactive species, which added to double and triple bonds to form [M + C3H5N]+• ions. Their collisional activation in an ion trap provided fragments helpful in localizing the multiple bond positions. This approach was applied to fatty acids with isolated, cumulated, and conjugated double bonds and triple bonds. The fatty acids were isolated from the fat body of early-nesting bumblebee Bombus pratorum and seeds or seed oils of Punicum granatum, Marrubium vulgare, and Santalum album. Using the method, the presence of the known fatty acids was confirmed, and new ones were discovered.
Highlights
The localization of double and triple bonds (DBs and TBs) is a key step in the structural characterization of fatty acids (FAs)
The chromatographic separation of FAs and their methyl esters (FAMEs) was achieved on the Develosil RP-Aqueous
The diagnostic peaks corresponding to cleavages before the first and after the last unsaturated bond in polyunsaturated FAMEs tended to be more abundant than the others
Summary
The localization of double and triple bonds (DBs and TBs) is a key step in the structural characterization of fatty acids (FAs). The collision activation of the adducts induced cleavages of C–C bonds next to the original double bond, leading to pairs of diagnostic fragments indicating the double bond position The advantage of this approach lies in its simplicity: the only requirement for an HPLC/APCI-MS2 method is the presence of acetonitrile in the mobile phase. Some plant FAs contain triple and double bonds conjugated, e.g., pyrulic acid (FA 17:2n-7,9TB ), ximenynic ( termed santalbic) acid (FA 18:2n-7t,9TB ), or heisteric acid (FA 18:3n-7t,9TB ,11c) from Heisteria silvanii seed oil [32]. Santalbic acid (FA 18:2n-7t,9TB ), identified for the first time in Santalum album [58,63], is one of the few acetylenic FAs occurring at higher levels in plants It is found in the seed oils of the Santalaceae, Olacaceae, and Opiliaceae families, where it can reach up to 95% of the total FAs [71,72]. To the best of our knowledge, the localization of triple bonds in FAMEs by RP-HPLC with MS detection is reported here for the first time
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