Liquid chromatography/mass spectrometry (LC/MS) with atmospheric pressure chemical ionization has been successfully applied to the simultaneous analysis of free brassinosteroids (polyhydroxylated steroids that serve as plant growth regulators) as their naphthaleneboronates. Of a range of analytical conditions that were tested, optimum results were obtained by the use of reversed-phase high-performance liquid chromatography using a mixture of acetonitrile and water. The positive-ion spectra of naphthaleneboronates of brassinosteroids showed pseudo-molecular ions, [M+H]+, and fragment ions corresponding to the losses of hydroxyl groups of the steroidal nucleus. The [M+H]+ ion was the most abundant for brassinolide and the [M+H−H2O]+ ions were the most abundant for castasterone, teasterone and typhasterol. Full-scan mass spectra were readily obtained from 400 ng of free brassinosteroids, while a limit of detection of 2 ng (signal-to-noise ratio 3) was attained in the selected-ion monitoring mode. The application of LC/MS to the study of brassinosteroids in a plant material is demonstrated by the analysis of seeds of Cannabis sativa L.
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Gamoh et al. (1996) studied this question.