Determination of glycyrrhetic acid in human plasma by LC–ESI–MS

A sensitive liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS) method for determination of glycyrrhetic acid, the active metabolite of glycyrrhizin, in human plasma using ursolic acid as the internal standard (IS) was established. Plasma was extracted with ethyl acetate and separated on a C18 column with a mobile phase of 10 mmol/l ammonium acetate–acetonitrile (10:90). Glycyrrhetic acid was determined using electrospray ionization in a single quadrupole mass spectrometer. HPLC–ESI–MS was performed in the selected ion monitoring (SIM) mode using target ions at m/z 469.5 for glycyrrhetic acid and m/z 455.5 for IS. Calibration curve was linear over the range of 0.1–400 ng/ml. The limit of quantitation for glycyrrhetic acid in plasma was 0.1 ng/ml. The mean plasma extraction recovery of glycyrrhetic acid was 94.51 ± 3.82%. The method has been successfully applied to study the pharmacokinetics of glycyrrhetic acid in healthy male Chinese volunteers. The assay was proved to be sensitive, accurate and convenient.