Simplified ultrasonically- and microwave-assisted solvent extractions for the determination of ginsenosides in powdered Panax ginseng rhizomes using liquid chromatography with UV absorbance or electrospray mass spectrometric detection

摘要

New approaches for the recovery of ginsenosides are presented that greatly simplify the liquid chromatographic(LC) determination of the total content of eight ginsenosides(Rb_1, Rb_2, Rc, Rd, Re, Rf, Rg_1 and Rg_2) in powdered Panax ginseng rhizomes. The extraction protocols not only recover the neutral ginsenosides, but also simultaneously incorporate base-catalyzed hydrolysis of the malonyl-ginsenosides using dilute potassium hydroxide added to the methanol-water extractant. This eliminates the need for an independent extraction step followed by acid- or base-catalyzed hydrolysis. Both ultrasonically-assisted and microwave-assisted extraction methods are developed. The optimization of these simplified methods to remove pendant malonate esters, while retaining the glycosidic linkages, was determined by LC through variation of the extraction/hydrolysis time, order of hydrolysis reagent addition, and evaluation of multiple extractions. A comparison of the ginsenoside profiles obtained with and without addition of base to the extractant solution was made using LCMS with positive-mode electrospray ionization(ESI~+) detection. A number of malonyl-ginsenosides were tentatively identified by their mass spectral fragmentation spectra and indicating that they were converted to the free ginsenosides by the new extraction/hydrolysis procedure.