Separation and Characterization of Triterpenoid Saponins in Gleditsia sinensis by Comprehensive Two-Dimensional Liquid Chromatography Coupled with Mass Spectrometry

A comprehensive two-dimensional liquid chromatography coupled with mass spectrometry method was established to separate and characterize triterpenoid saponins in Gleditsia sinensis, the Chinese herbal medicine Zhu-Ya-Zao used for the treatment of apoplexy. The saponins were separated on an Agilent Zorbax Eclipse plus C₁₈ column (2.1 mm × 150 mm, 1.8 µm) for the first dimension, and a Poroshell 120 phenyl-hexyl column (3.0 mm × 50 mm, 2.7 µm) for the second dimension. Methanol and acetonitrile were used as the organic mobile phase for ¹D and ²D, respectively. The theoretical peak capacity was 640, and the orthogonality was 57 %. Particularly, saponins with different numbers of monoterpene groups could be well separated on the second dimension. The structures were characterized by electrospray ionization tandem mass spectrometry in both positive and negative ion modes. In the MS/MS spectra, the relative abundances for [B α + Na]⁺ and [Y 0α + Na]⁺ were closely correlated with the number of sugar residues of the α-chain and β-chain, respectively, which facilitated the differentiation of isomers. Finally, a total of 72 saponins with molecular weights greater than 1500 Da were characterized. Among them, 49 compounds, including 2 acetylated saponins, were detected from G. sinensis for the first time.