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 (MS 2 ) and the ortho ‐quinoid [M – H – Me] ‐• radical anion thus formed then dissociates by loss of an extended series of neutral radicals, C n H 2n + 1 • ( n  = 0–16) from the long alkyl chain, in competition with the expulsion of CO and CO 2 (MS 3 ). The further fragmentation (MS 4 ) of the [M – H – Me – C 3 H 7 ] − ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M – H – Me – CO] ‐• and [M – H – Me – CO 2 ] ‐• ions provide some mechanistic and structural insights.