Simultaneous Determination of Magnesium Isoglycyrrhizinate and Its Active Metabolite 18 alpha-Glycyrrhetinic Acid in Rat Plasma by UPLC-MS-MS

A simple, reproducible, rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS-MS) method was developed for simultaneous determination of magnesium isoglycyrrhizinate (MgIg) and its active metabolite 18 alpha-Glycyrrhetinic acid (18 alpha-GA) concentration in rat plasma with clopidogrel as internal stand (IS). Multiple reaction monitoring (MRM) with positive scan mode, were set at m/z 823.67/453.50, m/z 471.31/177.14, and 322.20/212.15 for MgIg, 18 alpha-GA and IS, respectively. The intra- and inter-day precision(RSD) at four QC levels were both less than 15% and accuracies ranged from 93.6 to 112.7% for MgIg, and ranged from 94.6 to 108.2% for 18 alpha-GA. We successfully set up a reproducible, novel, sensitive, facile LC-MS-MS method for simultaneous detection of MgIg and 18 alpha-GA with the low limit of quantification (LLOQ) of 4.0 ng/mL for MgIg and 2.0 ng/mL for 18 alpha-GA. Although magnesium ion interfered with determination, we improved the sensitivity of 2.5 times for GL and 5 times for GA, when compared with reported method of Glycyrrhizin acid (GL) and GA. MgIg, 18 alpha-GA and IS were extracted with simple and convenient liquid-liquid extraction of methanol rather than relatively complicated and expensive solid-phase extraction (SPE). The validated method was successfully applied to pharmacokinetic study in rat plasma after intravenous administration of MgIg injection.