Simultaneous determination of 18 α ‐ and 18 β ‐glycyrrhetic acid in human plasma by LC‐ESI‐MS and its application to pharmacokinetics

A highly sensitive and selective LC‐ESI‐MS was developed, validated for the simultaneous determination of 18 α ‐glycyrrhetic acid ( α ‐GA) and 18β‐glycyrrhetic acid ( β ‐GA) for pharmacokinetic studies in healthy subjects. Sample preparation was performed by liquid–liquid extraction with ethyl acetate and the separations were achieved using a C 18 column with the mobile phase composed of 10 mmol/L ammonium acetate solution–methanol–acetonitrile (40:36:24, v/v/v) at a flow rate of 1 mL/min. The internal standard was honokiol and the epimers were quantified using a single quadrupole mass spectrometer employing ESI in the negative ion mode. The separation factor, α , was 1.512 for α ‐ and β ‐GA. The standard curves were linear for both epimers with coefficients of determination ( r  ≥ 0.9998) over the concentration range of 1–150 ng/mL. The precision and accuracy were ≤ 4.33 and ≤ 6.57%, respectively. The mean plasma extraction recoveries were 82.23 ± 1.91 and 84.29 ± 2.09% for α ‐GA and β ‐GA, respectively. The assay was successfully applied to evaluation of the pharmacokinetic properties of α ‐GA and β ‐GA from 19 volunteers who had received oral administration of diammonium glycyrrhizinate capsules. The initial data suggest that glycyrrhizin metabolizes to glycyrrhetic acid fairly slowly and the elimination of α ‐GA is slower than that of β ‐GA. Copyright © 2008 John Wiley & Sons, Ltd.