Determination of total glycyrrhetic acid in Glycyrrhizae Radix by second derivative UV spectrometry

Abstract

Second derivative (D2) spectrometry using ion-pair extraction technique was developed for the determination of total glycyrrhetic acid (GA) in Glycyrrhizae Radix. Glycyrrhizin (G) obtained from Glycyrrhizae Radix was hydrolyzed into GA in 2 N-HCl and methanol (1∶1) and extracted from aqueous phase in the form of an ion-pair complex with tetrapentylammonium bromide (TPA) as a counter ion. Maximum D2 amplitude (Z value) was obrained when 1000-fold or greater molar ratio of TPA was used at pH 11. Reaction time, temerature and ionic strength did not affect ion-pair formation. Dichloromethane was an effective extraction solvent of the ion-pair complex. The linearity of standard curve of ion-pair GA was obtained in the range of 4–120 μg/ml as GA. Assayed contents of GA in dry powder by D2 UV spectrometry and HPLC method were 5.31±0.04% and 5.20±0.008%, respectively.