The fragmentation of methyl abscisate and its 2E isomer in methane positive and negative chemical ionization mass spectrometry

Abstract

The fragmentation pathways of methyl abscisate and its 2E isomer in methane positive ion chemical ionization (PICI) and methane negative ion chemical ionization (NICI) mass spectrometry have been elucidated using isotopically labelled analogues. It is shown that in PICI the most abundant ions are formed by the loss of water, methanol, both methanol and water and of methyl formate. The PICI mass spectrum of methyl 2E abscisate differs significantly in that the loss of water is much less important. In NICI, the most abundant ions from methyl abscisate are due to the molecular anion, [M – H2O]− and [M – CH3OH]−. It is shown, however, that the methyl ester methyl is not lost in this last fragmentation. Two other significant ions contain the side chain and the ring of methyl abscisate, respectively. In contrast, the NICI mass spectrum of methyl 2E abscisate differs principally in showing an abundant loss of a hydrogen atom.