Untargeted profiling of Glycyrrhiza glabra extract with comprehensive two-dimensional liquid chromatography-mass spectrometry using multi-segmented shift gradients in the second dimension: Expanding the metabolic coverage

Metabolic profiling of Glycyrrhiza glabra using comprehensive two-dimensional liquid chromatography (LC × LC) coupled with photodiode array (PDA) and mass spectrometry (MS) detection is described. The separation was conducted under reversed-phase conditions, using a combination of first dimension (¹D) 150 mm microbore cyano column utilising 2.7 μm diameter (d_p) particles, and second dimension (²D) 50 mm superficially porous octadecylsilica column with 2.7 μm d_p particles. A multi-segmented shift gradient (MSG) for the ²D separation was developed, and the orthogonality achieved was compared with other modes of gradients, such as full in-fraction, and shift gradient systems. Results demonstrated a significant expansion of metabolic coverage using MSG in ²D, providing the highest measure of orthogonality compared to other gradient modes. Compound identifications were performed by employing complementary data from PDA and MS detection, with reference to structural group-type distribution in 2D space. A total of ca. 120 compounds were detected, and among them 37 were tentatively identified, distributed over the chemical families of glycosylated flavanones, triterpene saponins, and others. In comparison with one-dimensional LC, the total number of compounds detected was ca. 2-fold greater when LC × LC was employed. To the best of our knowledge, this is the first demonstration of the MSG mode in LC × LC, representing a powerful strategy to expand the metabolic coverage for analysis of plant-derived extracts, containing a multitude of different phytochemical classes.