Quantitative Determination of Steroidal Saponins from Dioscorea Species and Dietary Supplements using UHPLC-PDA-ELSD

Yam (Dioscorea spp.) is an important tuber plant for edible and medicinal use to promote health and longevity in Chinese tradition [1]. Steroidal saponins were reported to be the major physiologically active constituents in yam [2]. Furostanol and spirostanol glycosides, two main steroidal saponins, have been found in many types of yams (Dioscorea species) [3].

Ultra high-performance liquid chromatography (UHPLC) with UV and ELS detection was used for the quantification of steroidal saponins from roots and rhizomes of Dioscorea species and dietary supplements claiming to contain Dioscorea. The analysis was performed on a Waters Acquity UPLC system with an Acquity UPLC BEH Shield RP18 column using gradient elution with water and acetonitrile, both containing formic acid. Owing to their low UV absorption, the steroidal saponins were detected by evaporative light scattering. The twelve saponins could be separated within 15 minutes using UPLC method with detection limits of 5 – 12 µg/mL. The analytical method was validated for linearity, repeatability, limits of detection (LOD) and limits of quantification (LOQ). The RSDs for intra- and inter-day experiments were less than 3.0%, and the recovery efficiency as 97 – 101%. The total content of saponins was found to be in the range from 0.02 – 14.5% and 0.2 – 10.5% (w/w) in samples of Dioscorea and dietary supplements, respectively. UHPLC-mass spectrometry with a quadrupole mass analyzer and ESI source was used for confirmation of the identity of saponins. The developed method is simple, economic, rapid and especially suitable for quality control analysis of steroidal saponins.

Fig. 1. Comparison of UPLC-ELSD profiles of Dioscorea species

Acknowledgements: This research is supported in part by the National Center for Complementary and Alternative Medicines (NCCAM), the Office of Dietary Supplements (ODS) and the National Cancer Institute (NCI) Grant Number P50AT006268. Additional support was also provided by the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58 – 6408 – 02 – 1-612, and the authors would like to thank Annette Ford for the extractions of plant samples. References: [1] Liu SY, et al. (1995)J Chin Med, 6: 111 – 126. [2] Hu K, et al. (1996) Planta Med, 62: 573 – 575. [3] Zhu J, et al. (2010)J Pharm Biomed Anal, 53: 462 – 474.