Development of an Efficient HPLC Fluorescence Detection Method for Brassinolide by Ultrasonic-Assisted Dispersive Liquid–Liquid Microextraction Coupled with Derivatization

A novel hyphenated technique based on ultrasonic-assisted dispersive liquid–liquid microextraction (UA-DLLME) coupled with derivatization has been established for the determination of brassinolide (BL, a representative of brassinosteroids) by HPLC fluorescence detection. 9-Phenanthreneboronic acid is used as labeling reagent of BL. UA-DLLME parameters containing type and volume of extraction and disperser solvent, pH and ultrasonication time are optimized. Derivatization parameters are optimized included amount of 9-phenanthreneboronic acid, volume ratio of pyridine, derivatization time and temperature. Under optimal conditions, quantitative linear range of BL is 50–1,000 ng L −1 and excellent linear response is observed with correlation coefficient of 0.9996. Limit of detection and limit of quantification are calculated as 8.0 and 25.0 ng L −1 , respectively. RSDs of retention time and peak area are in the range of 0.68–0.97 % and 4.61–6.54 % for intra-day precision, 1.32–1.94 % and 7.28–9.75 % for inter-day precision, respectively. Accuracy is satisfactory in the range of 82.3–125.1 %. RSDs’ values of repeatability are in the range of 0.82–1.79 and 3.95–8.53 % for retention time and peak area, respectively. Enrichment factor for BL is 189. The results of recovery and matrix effect are in the range of 82.0–108.6 and 90.0–115.3 %, respectively. The proposed method has been applied for the determination of BL in Arabidopsis thaliana , Daucus carota and Brassica campestris L. leaves with much higher sensitivity than many other methods.