The unusual fragmentation of long-chain feruloyl esters under negative ion electrospray conditions.

Long-chain ferulic acid esters, such as eicosyl ferulate (1), show a complex and analytically valuable fragmentation behavior under negative-ion electrospay collision-induced dissociation ((-)-ESI-CID) mass spectrometry, as studied by use of a high-resolution (Orbitrap) mass spectrometer. In a strong contrast to the very simple fragmentation of the [M + H]+ ion, which is discussed briefly, the deprotonated molecule, [M - H]- , exhibits a rich secondary fragmentation chemistry. It first loses a methyl radical (MS2 ) and the ortho-quinoid [M - H - Me]-• radical anion thus formed then dissociates by loss of an extended series of neutral radicals, Cn H2n+1 • (n = 0-16) from the long alkyl chain, in competition with the expulsion of CO and CO2 (MS3 ). The further fragmentation (MS4 ) of the [M - H - Me - C3 H7 ]- ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M - H - Me - CO]-• and [M - H - Me - CO2 ]-• ions provide some mechanistic and structural insights.