LIQUID-CHROMATOGRAPHY ELECTROSPRAY-IONIZATION TANDEM MASS-SPECTROMETRY - A TOOL FOR THE IDENTIFICATION AND QUANTIFICATION OF ABSCISIC-ACID GLUCOSYL ESTER

LC/ESI-tandem MS techniques have been applied to the analysis of endog enous abscisic acid glucosyl ester (ABA-GE). By parent ion scanning (m /z 263) and constant neutral loss (162 u) experiments, endogenous ABA- GE could be identified in extracts from wilted leaves of Phaseolus vul garis L. cv. Jutta. Using ABA-[6'D-2]GE as internal standard, the endo genous content of ABA-GE in wilted leaves of Phaseolus vulgaris L. cou ld be estimated by parent ion scanning of m/z 263. From the signals of the [M-H](-)-ions of ABA-GE (m/z 425) and ABA-[6'-D-2]GE (m/z 427) ob tained, the amount of the endogenous conjugate was calculated to be 28 0 +/- 9 ng ABA-GE/g plant material. This is the first accurate method for the direct quantification of ABA-GE as intact compound at endogeno us levels.