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 re-garding 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(Rb1, Rb2, Rb3, Rd, Re, Rf and Rg1), 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 CH 3 OH 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 Rb1 was also carried out, and consistent content results were obtained in DART-MS and high-performance liquid chromatography(HPLC).