CONTINUOUS AND STOP-FLOW APPROACHES IN COMPREHENSIVE TWODIMENSIONALLIQUID CHROMATOGRAPHY

Complex real-world samples demand advanced analytical techniques to tackle such chromatography challenges. Among them, multidimensional liquid chromatography (MD-LC), by virtue of its increased resolving power represents a potential solution. MD-LC can be operated either in offline or online mode. On the one hand, in the offline mode, fractions eluted from first dimension (D1) are collected, separated from solvent by evaporation, re-dissolved and reinjected in the second dimension (D2). On the other hand, in the online approach, the transfer between the two dimensions is fully automated, usually by means of electronically controlled switching valves. Online techniques are more convenient when dealing with limited sample amounts but they are more difficult to realize and require dedicated instrumentation and software. Within the MD-LC techniques, a further distinction is represented by heart-cutting LC where only a few selected fractions are transferred from D1 to D2 and comprehensive LC (LC× LC), where the entire sample is subjected to the 2D advantage. LC×LC can be performed under either continuous or stop-flow conditions. In both cases, all fractions are transferred from D1 to D2, being the whole sample analyzed in both dimensions. In this contribution, applications of both LC×LC approaches are discussed to suit specific separation tasks. In addition, examples of UHPLC (ultra high pressure liquid chromatography) methods and miniaturized LC systems for high efficient analyses, and negligible solvent/time consumption, respectively, are illustrated.