HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY OF GIBBERELLINS

Seven tetracyclic monocarboxylic acid gibberellins (GA1, GA3, GA4, GA5, GA7, GA9 and GA30) and the methyl ester derivatives of GA1, GA3, GA4, GA7 and GA9 were analyzed using combined high-performance liquid chromatography-thermospray mass spectrometry or direct injection thermospray mass spectrometry. The seven free acid GAs were resolved using a 25-min water-acetonitrile (0.1 M ammonium acetate) gradient mobile phase and a 5-mu-m, 150 mm x 4.6 mm, ODS column. Positive-ion thermospray mass spectra of these compounds typically showed intense [M + NH4]+ ions and few, if any, fragment ions. In the negative-ion mode (filament on) the free acid GAs showed [M - H]- or [M + HCO2] - ions as the base peaks. Negative-ion spectra of the methyl ester GAs showed the [M + HCO2]- ions, however, the base peaks were [M]-. or [M + HCO2H] - ions attributed to electron capture processes. Thermospray tandem mass spectra were obtained for GA1, GA3 and GA30 from the collisionally activated dissociation (CAD) of their [M + NH4]+ ions. The CAD mass spectra show differences which allow the differentiation of the isomers GA3 and GA30 without the chromato-graphic separation. The daughter ions resulting from fragmentation processes corresponded to varying losses of CO, CO2, ammonia and water.