Theoretical Guiding Principles for Two-Dimensional Liquid Chromatography

A small number of foundational principles lie at the heart of decision making when developing useful two-dimensional liquid chromatography (2D-LC) methods. This includes the concept of 2D peak capacity, usage of the 2D separation space, undersampling the first dimension separation, and detection sensitivity of the 2D method. These concepts are frequently discussed in the context of comprehensive 2D-LC, but they can also be used as guiding principles when developing non-comprehensive methods (i.e., mLC-LC and sLC×LC). In this chapter we introduce each of these concepts, briefly summarize the relevant literature, and discuss the implications for method development in practical terms. A holistic appreciation of the ideas is especially important when optimizing 2D-LC methods due to the tradeoffs between different metrics of separation performance (e.g., peak capacity and detection sensitivity are usually opposing objectives).