LIQUID-CHROMATOGRAPHY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY FOR ANALYZING PLANT HORMONE CONJUGATES

A series of synthetic gibberellin glycosyl esters and abscisic acid gl ucosyl ester were investigated using LC-electrospray ionization (ESI) MS (negative- and positive-ion modes). From the spectra obtained, diag nostic ions were chosen to monitor HPLC separations on RP-18. The abun dant [M + Na](+) ion of the positive-ion ESI spectra enables sugar est ers to be recognized from their molecular masses. Under negative-ion E SI conditions, the [M - sugar](-) ion as the base peak allows one to s earch for a group of different sugar esters of a distinct aglycone. Un der selected-ion monitoring conditions (positive-ion ESI), less as 3 . 10(-2) ng of abscisic acid glucosyl ester could be detected. The acce ssibility of ESI-MS results together with characterization by retentio n properties obtained by HPLC qualify LC-ESI-MS as a powerful method f or the analysis of intact plant hormone conjugates, especially glucosy l ester, at endogenous levels.