Ionic liquid–lithium salt based microwave pretreatment followed by ultrasonic-assisted extraction of syringin and oleuropein from Syringa reticulata var. mandshurica branch bark by a dual response surface methodology

Abstract

Rapid and efficient solvent extraction of syringin and oleuropein from Syringa reticulata var. mandshurica branch bark was achieved using microwave-assisted ionic liquid–lithium salt pretreatment, followed by ultrasonic breakdown of the plant cell walls. The conditions for this novel sample treatment method, including microwave pretreatment time and power, ultrasound irradiation extraction time and power, types and concentrations of ionic liquid and lithium salt, and the liquid–solid ratio, were optimized using a dual response surface methodology. The proposed approach under optimal conditions was compared with conventional extraction methods. No degradation of syringin and oleuropein was observed in stability studies performed with a reference standard. The experimental results indicate that the proposed approach is a simple and efficient sample preparation technique that has strong potential for application in the field of sample analysis.