Design and performance evaluation of ionic liquid-based microwave-assisted simultaneous extraction of kaempferol and quercetin from Chinese medicinal plants

Abstract

An ionic liquid-based microwave-assisted extraction (IL-MAE) technique has been successfully developed for the simultaneous effective extraction of quercetin and kaempferol from Toona sinensis and Rosa chinensis which are Chinese medicinal plants. Twenty different types of ionic liquids (ILs) with different cations and anions have been synthesized and investigated. Several significant operating parameters of IL-MAE were optimized by a series of single factor experiments and orthogonal design L₉ (3⁴) experiments, respectively. Compared with ionic liquid-based maceration extraction (IL-ME), ionic liquid-based heat extraction (IL-HE) and ionic liquid-based ultrasound-assisted extraction (IL-UAE), the optimized approach was demonstrated as the optimal technique with the highest extraction efficiency and the shortest extraction time. Reversed phase high performance liquid chromatography (RP-HPLC) with ultraviolet-detection (UV-DAD) was employed for the simultaneous analysis of kaempferol and quercetin. The results indicated that the extraction amounts of quercetin from Toona sinensis extracted using [Bmim]Br and from Rosa chinensis extracted using [Omim]Br were 176.5 mg g⁻¹ with RSD 1.2% and 134.3 mg g⁻¹ with RSD 0.63%. And the extraction amounts of kaempferol from Toona sinensis extracted using [Bmim]Br and from Rosa chinensis extracted using [Omim]Br were 16.12 mg g⁻¹ with RSD 0.24% and 9.070 mg g⁻¹ with RSD 0.15%. The developed approach for analyzing quercetin was linear between the concentrations of 32.10 mg L⁻¹ to 233.3 mg L⁻¹ in Toona sinensis and 25.70 mg L⁻¹ to 160.5 mg L⁻¹ in Rosa chinensis with the regression coefficients (R) of 0.9998 and 0.9999, respectively. And for kaempferol, the developed approach was linear between the concentrations of 0.73 mg L⁻¹ to 23.20 mg L⁻¹ in Toona sinensis and 0.19 mg L⁻¹ to 15.00 mg L⁻¹ in Rosa chinensis with the regression coefficients (R) of 0.9993 and 0.9996, respectively. The recoveries of quercetin extracted by the developed methods were 96.76–104.1% in Toona sinensis and 98.40–103.3% in Rosa chinensis, and the recoveries of kaempferol were 95.75–106.3% in Toona sinensis and 98.55–102.9% in Rosa chinensis with the RSDs of lower than 3.0%. The LODs were 1.87–2.26 μg mL⁻¹. The microstructures and chemical structures of these two researched samples before and after different extraction procedures were also investigated.