A vacuum assisted dynamic evaporation interface for two-dimensional normal phase/reverse phase liquid chromatography

A vacuum assisted dynamic solvent evaporation interface for coupling of two-dimensional normal phase/reverse phase liquid chromatography was developed and evaluated. A normal-phase liquid chromatographic (NPLC) column of a 250 mm × 4.6 mm I.D. 5 μm CN phase was used as the first dimension, and a reversed-phase liquid chromatographic (RPLC) column of 250 mm × 4.6 mm I.D. 5 μm C18 phase was used as the second dimension. The eluent from the first dimension flowed into a fraction loop, and the solvent in the eluent was dynamically evaporated and removed by vacuum as it was entering the fraction loop of the interface. The non-evaporable analytes was retained and enriched in about 5–25 μL solution within the loop. Up to 1 mL/min of mobile phase from the first dimension can be evaporated and removed dynamically by the interface. The mobile phase from the second dimension then entered the loop, and dissolved the concentrated analytes retained inside the loop, and carried them onto the second dimension column for further separation. The operation conditions of the two dimensions were independent from each other, and both dimensions were operated at their optimal chromatographic conditions. We evaluated the interface by controlling the loop temperature in a water bath at normal temperature, and investigated the sample losses by using standard samples with different boiling points. It was found that the sample loss due to evaporation in the interface was negligible for non-volatile samples or for components with boiling point above 340 °C. The interface realizes fast solvent removal of mL volume of fraction and concentration of the fraction into tenth of μL volume, and injection of the concentrated fraction on the secondary column. The chromatographic performance of the two-dimensional LC system was enhanced without compromise of separation efficiency and selectivity on each dimension.