Optimization of Extraction Methods for Flavonoids in Onion by RP-HPLC–DAD

An orthogonal experiment L9(33) for evaluation of the extraction of flavonoids from onion by hot water extraction method, ethanol extraction method, and ultrasonic extraction method and their determination by means of ultraviolet–visible spectroscopy was carried out. The main orders for the affecting factors in three methods were as following during the extraction process: (a) hot water extraction method: the extraction time > the proportion of liquid and materials > the extraction temperature; (b) ethanol extraction method: the extraction temperature > the extraction time > the proportion of liquid and materials; and (c) ultrasonic extraction method: the extraction time > solvent volume fraction > the proportion of liquid and materials. The results showed that the ethanol extraction method was determined the best extraction method, and the best extraction results were obtained when the samples were determined by a reversed-phase high performance liquid chromatographic method with a diode array detector (RP-HPLC–DAD) for each method. A reversed phase EclipseXDB-C18 column and isocratic elution were used during the analysis, and the detection wavelength was set at 270 nm. In addition, the method was thoroughly validated; its precision (as RSD) ranged from 0.22% to 0.31%, and satisfactory recoveries varied between 98.67% and 99.66%.