Vacuum-evaporation Interface of Comprehensive Two-dimensional Liquid Chromatography and Its Application

A comprehensive two-dimensional liquid chromatographic system was developed using a vacuum-evaporation interface (VEI). A normal-phase liquid chromatography (NPLC) with a CN microcolumn was used as the first dimension (1st-D), and a reversed-phase liquid chromatography (RPLC) with a C18 monolithic column was used as the second dimension (2nd-D). A two-position, ten-port valve with two identical storage loops was used as the interface that enabled alternate sampling of the first column eluent onto the second column until the analysis was finished. In one of the two positions, the eluent from the first column filled one of the loops and was evaporated at 25 °C under vacuum leaving the analyses to stick onto the inner wall of the loop. When the valve was switched to the second position, the effluent from the first column flowed through the other loop, whereas mobile phase of the 2nd-D dissolved the analyses in the loop from the previous cycle and injected them onto the second column allowing online solvent exchange of the fractions from the 1st-D to the 2nd-D. The utility of the comprehensive 2D-LC system was demonstrated in the analysis of standard samples and traditional Chinese medicine Cnidium monnieri (L.) Cuss extract.