Detection of Saponins and Oligosaccharides in Herbs Using Direct Analysis in Real-time Mass Spectrometry

The use of direct analysis in real-time(DART) mass spectrometry(MS) for direct detection of saponins and oligosaccharides is difficult mainly because of the strong polarity of these molecules, which results in challenges regarding desorption and ionization of the compounds. Structure derivatization, such as methylation, is essential for improving the volatility and the proton affinity of saponin and oligosaccharides. In this study, solid-phase methylation of saponins and oligosaccharides was accomplished in a stainless steel methylation column, and the methylated products of astragaloside, salidroside, icariin, ginsenosides(Rbl, Rb2, Rb3, Rd, Re, Rf and Rgl), maltose, isomaltose, sucrose and maltotriose were analyzed using DART-MS. Fragmentations occurred during ionization and tandem mass spectrometry, and most fragments corresponded to the glycosidic bond, cross-ring cleavages, and the neutral loss of CH3OH ions, but the aglycone cleavage fragment was not detected. Furthermore, the method was successfully used in the rapid and simultaneous analysis of saponins and oligosaccharides in a ginseng extract; quantitative analysis of ginsenoside Rbl was also carried out, and consistent content results were obtained in DART-MS and high-performance liquid chromatography(HPLC).