Control of the Selectivity of the Separation of Dicaffeoylquinic Acids in Reversed-Phase Chromatography

The chromatographic behavior (change in the logarithm of the retention factor with a change in the composition of the mobile phase) of dicaffeoylquinic (DCQ) acids is determined by the chromatographic behavior of monocaffeoylquinic acids. The most efficient combination is the conventional C18 stationary phase (Kromasil) and environmentally friendly mobile phases, in which acetonitrile is replaced by 2-propanol, with the mobile phase acidified with 0.25 vol % of phosphoric acid to stabilize the charge form of acids. The retention of dicaffeoylquinic acids can be explained by the simultaneous adsorption of caffeic acid substituents by two aromatic rings for both studied organic modifiers of the mobile phase. The replacement of the C18 phase by the phenylhexyl phase did not lead to significant changes in the selectivity of the separation of isomeric DCQ acids. At the same time, not all isomers were separated using mobile phases based on both organic modifiers: acetonitrile and 2-propanol. The developed conditions for the separation of DCQ in the gradient mode with “green” eluents A (10 vol % of isopropanol and 0.25 vol % of phosphoric acid in water) and B (20 vol % of isopropanol and 0.25 vol % of phosphoric acid in water) were used to determine the species composition of caffeoylquinic acids in coffee, mate, and artichoke tea.