Determination of brassinosteroids in the sub-femtomolar range using dansyl-3-aminophenylboronate derivatization and electrospray mass spectrometry.

A selective and sensitive electrospray ionization (ESI) mass spectrometry based method for detection of brassinosteroids (BS) in plant samples was developed. The limit of detection (LOD) was dramatically reduced over existing analytical methods using a microbore (1.00 mm) C18 column and chemical derivatization of free BS to dansyl-3-aminophenylboronates. The LOD in the selected-ion monitoring (SIM) mode for derivatized BS was 125 attomole (signal-to-noise ratio 3). The practical utility of the method is documented in Arabidopsis thaliana plant transformation of castasterone to brassinolide using a deuterium-labeled precursor. The method could be very useful for the detection of native BS in plant tissue and biosynthetic studies. Copyright 2004 John Wiley & Sons, Ltd.