Development of a comprehensive two-dimensional hydrophilic interaction chromatography/quadrupole time-of-flight mass spectrometry system and its application in separation and identification of saponins from Quillaja saponaria

Hydrophilic interaction chromatography (HILIC) was used in two dimensions in a comprehensive two-dimensional HILIC hyphenated with a quadrupole time-of-flight mass spectrometry (HILIC × HILIC-Q-TOF-MS) system for the analysis of complex samples of hydrophilic compounds. A TSKgel Amide-80 column was employed as the first dimension, and a short PolyHydroxyethyl A column was as the second dimension. The column system showed moderate orthogonality at defined operational conditions. A high speed Q-TOF-MS detector as a third complementary dimension significantly improved the peak capacity. The separation capability of the developed HILIC × HILIC-Q-TOF-MS system was tested by separating an extract from Quillaja saponaria. The major components, quillaja saponins, in the extract were well identified by means of [M − H]− ions, characteristic product ions, and their two-dimensional retention behaviors. Several pairs of isomers, which were often co-eluted on conventional LC–MS methods and had similar fragmentation characteristics in MS/MS spectra, were well separated on the two-dimensional system based on their different hydrophilicity. The developed comprehensive two-dimensional HILIC system demonstrates unique selectivity for hydrophilic compounds and satisfactory peak capacity and resolution for analogues by making sufficient use of two-dimensional separation plane.