Rapid Determination of Endogenous 20-Hydroxyecdysone in Plants on MALDI-TOF/TOF Mass Spectrometry via Chemical Labeling Based on Boronate Affinity

20-Hydroxyecdysone (20E) derived from plants has a wide range of physiological and pharmacological effects on animals and humans, and rapid and sensitive methods for screening of the endogenous 20E in plants are thus required. Herein, a matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS) method is described for rapid and sensitive determination of endogenous 20E in plants. It is based on the use of the (3-(acridin-9-ylamino) phenyl) boronic acid (AYPBA) as the mass tag to assist the MS and tandem MS (MSn) analysis of 20E on MALDI-TOF/TOF MS. Good linearity was obtained with a determination coefficient (R2) larger than 0.99 in the range of 0.025–2.5 μΜ. The limit of detection (LOD) was 2.4 fmol. Acceptable precision and accuracy were gained by intra- and inter-day analysis with relative standard deviations less than 19.5% and relative recoveries ranging from 85.7 to 105.2%. In addition, the AYPBA labeled 20E produced abundant characteristic fragment ions under the high energy collision-induced dissociation, which facilitated the identification of 20E by MS2 analysis on MALDI-TOF/TOF MS. Using the method, we enabled the identification and quantification of endogenous 20E in four herbs including Cyanotis arachoidea, Achyranthes bidentata, Spinacia oleracea and Chenopodium quinoa willd., demonstrating the feasibility of the proposed method for screening of the endogenous 20E in plants.