Online polymer monolith microextraction with in-situ derivatization for sensitive detection of endogenous brassinosteroids by LC-MS

An automatic and sensitive method which integrated polymer monolith microextraction and in-situ derivatization with liquid chromatography-mass spectrometry (PMME-ISD-LC-MS) was proposed for the quantification of endogenous brassinosteroids (BRs) in plant samples. In the described method, the anionic HIILIC monolithic column was modified with 2-methyl-4-phenylaminomethylphenylboronic acid (2-methyl-4-PAMBA) through ion exchange interaction and then used as a boronate affinity media to selectively capture, purify and derivatize BRs in crude extract through the reaction of the boronic acid group of 2-methyl-4-PAMBA and cis-diol on BRs. The BR derivatives were easily eluted by destroying the ion exchange interactions using the acidic eluting solvent, and then analyzed by LC-MS. The whole extraction and LC-MS analysis processes were automatically controlled which could be completed within 50 min. Under the optimized conditions, good linearities were obtained for six BRs with the correlation coefficients (R) ranging from 0.9953 to 0.9998. The limits of detection (LODs, S/N = 3) ranged from 0.10 to 1.29 pg mL(-)(1). The recoveries were between 82.3% and 119.1% with the relative standard deviations (RSDs) ranging from 2.2% to 18.3%. Finally, the proposed method was applied for the quantification of endogenous BRs in various plant samples including different Oryza sativa L. cv. tissues (1.0 mg, fresh weight (FW)), Phaseolus vulgaris L. (1.0 mg FW), Vigna unguiculata (1.0 mg FW), Arabidopsis thaliana flower (1.3 mg FW).