Ag. Netting et Ro. Lidgard, Fragmentation of methyl abscisate and pentafluorobenzyl abscisate in methane electron capture negative ionization tandem mass spectrometry, J MASS SPEC, 34(6), 1999, pp. 611-621
The methyl and pentafluorobenzyl esters of the plant hormone abscisic acid
were subjected to methane chemical ionization tandem mass spectrometry (MS/
MS). The spectra obtained allow the unambiguous identification of abscisic
acid in a few milligrams of plant material, In full-scan mode pentafluorobe
nzyl (PFB) abscisate (ABA) gave three significant ions at m/z 263 ([M - PFB
](-)), m/z 219 ([M - PFB - CO2](-)) and m/z 153 ([M - PFB - side chain](-))
. Each of these was subjected to MS/MS and structures were assigned to the
product ions using the labelled analogues, PFB[1'-O-18]ABA, PFB[4'-O-18]ABA
, PFB[side-chain-H-2(4)]ABA and PFB[ring-H-2(6)]ABA. Similarly, in full-sca
n mode, methyl abscisate gave three significant ions at m/z 278 (M-), m/z 2
60 ([M - H2O](-)) and m/z 245 ([M - H - CH3OH](-)) and in MS/MS the use of
the methyl esters of the above labelled analogues, and [H-2]methyl abscisat
e, allowed structures to be assigned to the product ions. Using these resul
ts it will be possible to dissect abscisic acid so that most labelled atoms
from C-13-labelled substrates will be able to be uniquely identified from
a few nanograms of C-13-labelled abscisic acid. If sufficient incorporation
of C-13-labelled substrates can be obtained it should be possible to inves
tigate the pathway(s) of abscisic acid biosynthesis using less than 1 g of
plant material. Copyright (C) 1999 John Wiley & Sons, Ltd.