Abstract:

Gynostemma pentaphyllum (Thunb.) Makino contains dammarane-type triterpenoid saponins, similar to ginseng, with a host of pharmacological activities. However, its planting resources and chemical composition are quite complex. The chemical constituents of Gynostemma pentaphyllum vary drastically among different origins and varieties. Thus, the corresponding quality control methods also need to be different. Currently, limited information is available about the quality control of Gynostemma pentaphyllum from Fujian. A new method based on ultra-high performance liquid chromatography-charged aerosol detection (UHPLC-CAD) was established for the determination of gypenoside XLVI and LVI in Gynostemma pentaphyllum. The major components of Gynostemma pentaphyllum were characterized using UHPLC-quadrupole time-of-flight-mass spectrometry (UHPLC-Q-TOF/MS) combined with UHPLC-CAD. The results revealed gypenoside XLVI, LVI, and their corresponding malonyl-containing acidic saponins as the main components. However, malonylgypenoside XLVI and LVI can easily remove their malonyl group and convert to gypenoside XLVI and LVI during the application of Gynostemma pentaphyllum. In this study, the samples were pretreated using alkali hydrolysis to transform the acid saponins completely, and the final contents of gypenoside XLVI and LVI were determined via UHPLC-CAD.

The optimal alkaline hydrolysis, extraction, and liquid chromatography conditions were established. First, the alkaline hydrolysis conditions were optimized. The effects of the volume of ammonia and reaction time on the contents of gypenoside XLVI, LVI, malonylgypenoside XLVI, and LVI were examined. Malonylgypenoside XLVI and LVI could be transformed completely to gypenoside XLVI and LVI by standing for 24 h in an ethanol-water-ammonia (50∶46∶4, v/v/v) mixture. Furthermore, the extraction conditions were optimized. Next, effects of the different solvents, extraction time, and solid-liquid ratio on the extraction rates of gypenoside XLVI and LVI were investigated. The extraction method for Gynostemma pentaphyllum powder using the ethanol-water-ammonia (50∶46∶4, v/v/v) and a solid-liquid ratio of 1∶150 (g∶mL) for 30 min was established. Finally, a prepared test solution was separated on a Waters ACQUITY UPLC BEH C18 chromatographic column (100 mm×2.1 mm, 1.7 μm). Acetonitrile and 0.1% (v/v) formic acid aqueous solution were used as the mobile phases for gradient elution. The flow rate was set to 0.5 mL/min and column temperature was maintained at 40 ℃. The separation was detected using a charged aerosol detector. Results indicated that the logarithm of the mass concentrations of gypenoside XLVI and LVI had a linear relationship with the logarithm of the peak area in the range of 9.94-318.00 μg/mL and 12.78-409.00 μg/mL, respectively. The correlation coefficients (r) were 0.9993 and 0.9995, respectively.

The limit of detection (LOD) and the limit of quantification (LOQ) of gypenoside XLVI were 1.58 μg/mL and 6.36 μg/mL, respectively. The LOD and LOQ of gypenoside LVI were 2.05 μg/mL and 8.18 μg/mL, respectively. The relative standard deviations (RSDs) of precision, repeatability, and 24 h stability were less than 2.0% (n=6). The spiked recoveries of gypenoside XLVI were 100.2%-107.2% and the RSD value was 2.4%. The spiked recoveries of gypenoside LVI were 97.9%-104.2% and the RSD value was 2.6%. The results of 16 batches of Gynostemma pentaphyllum samples indicated that the gypenoside XLVI content was 0.57%-2.57%, and gypenoside LVI content was 0.66%-2.99%. Hence, this method has high sensitivity and good reproducibility. Therefore, it can be used for quality research and quality control of Gynostemma pentaphyllum from Fujian.

Key words: ultra-high performance liquid chromatography-charged aerosol detector (UHPLC-CAD), gypenoside XLVI, gypenoside LVI, Gynostemma pentaphyllum (Thunb.) Makino from Fujian