Nonderivatized gibberellin glucosyl conjugates were analysed by capillary reversed-phase high-performance liquid chromatography/mass spectrometry. Positive as well as negative ion mass spectra were obtained by frit fast atom bombardment. The spectra were found to provide useful information for the identification and structural elucidation of the glucosyl conjugates.
I N T R O D U C T I O N
Gibberellins (GAS) are a group of diterpenoic acids, which act as endogenous growth regulators in plants.' They also occur as glucosidic conjugates, in which the glucose moiety is linked either to a hydroxyl group, resulting in a GA-0-glucoside or to the 7-carboxyl group yielding a GA glucosyl ester.
Quantitative and qualitative analysis of the methylated and silylated aglycons is achieved easily through the use of combined gas chromatography/mass spectrometry (GC/MS).' Permethylation of GA-O-glucosides also yields products suitable for analysis by GC/MS.3*4 However, the derivatization procedure cannot be applied to GA glucosyl esters since these compounds undergo transesterification under those condition^.^ Furthermore, the procedure is also laborious and time consuming.
Non-derivatized GA conjugates lack volatility and are relatively thermolabile, which makes traditional electron impact analysis difficult. The problem can be overcome by the use of soft ionization techniques.
Recently it has been shown that GAS and GA conjugates can be analysed by combined liquid chromatography/mass spectrometry (LC/MS) using an atmospheric pressure ionization interface (API).6 It has also been shown that static fast atom bombardment (FAB) mass spectrometry can provide useful structural information of GAS and GA conjugates.' However, it is difficult to use static FAB to analyse complex plant extracts containing trace amounts of GA conjugates, since the extracts, even after extensive purification, contain large amounts of impurities. This has led us to investigate the potential use of combined capillary frit-FAB LC/MS, which combines both a high-efficiency separation system and an appropriate ionization and