Determination of 18 beta-glycyrrhetic acid in human plasma by high-performance liquid chromatography

A sensitive high-performance liquid chromatographic method has been developed for the determination of 18 beta-Glycyrrhetic acid in human plasma. 18 alpha-Glycyrrhetic acid was used as an internal standard. The procedure includes pretreatment by liquid-liquid extraction and chromatographic separation on a reversed-phase column with ultraviolet detection. The detection limit of the drug was 5 ng/ml. The method was applied to the determination of 18 beta-glycyrrhetic acid in plasma after oral administration of a herbal medicine containing 18 beta-glycyrrhitic acid in human volunteers.