ANALYSIS OF BRASSINOSTEROIDS BY LIQUID-CH ROMATOGRAPHY MASS-SPECTROMETRY

A microanalytical LC/MS method for the determination of brassinosteroi ds as their boronates has been developed. Under reversed-phase liquid chromatographic conditions the brassinolide boronates, formed by napht haleneboronic acid, m-aminophenylboronic acid or dansylaminophenylboro nic acid, have been analyzed using atmospheric pressure chemical ioniz ation (APCI) and electrospray ionization (ESI) methods. The effects of additives to the liquid chromatographic mobile phase on the sensitivi ty for detection of the boronate were examined. A detection limit of 2 5 picogram (signal-to-noise ratio 3) of brassinolide as naphthalenebor onate was attained in the selected-ion monitoring (SIM) mode with elec trospray ionization, and that of 2.5 picogram (signal-to-noise ratio 4 ) for the naphthaleneboronate derivative was attained in the multiple reaction monitoring (MRM) mode with ESI. The LC/MS analysis of these b oronate derivatives could be very useful for trace analysis of brassin osteroids.