Comprehensive two-dimensional liquid chromatography

Despite progress in hardware and column technology, the complexity and heterogeneity of many samples still pose a challenge for state-of-the-art 1D liquid chromatography (LC). As an effective answer to these analytical questions, multidimensional comprehensive techniques have become an attractive strategy across disciplines. This Primer provides a general overview of 2D comprehensive LC (LC x LC), including hardware, software and best practices for experimentation. The underlying principles are described, alongside the requirements of separation and detection equipment. In addition, this Primer discusses data collection, processing and analysis, with an exploration of inherent challenges and possible workarounds. Selected examples are presented to show how the gain in resolution afforded by LC x LC has enabled in-depth characterization of complex non-volatile samples, such as pharmaceuticals, polymers, foods and the 'omics. Finally, the technique progress is evaluated, with an outline of future directions for the field. Using multiple liquid chromatography columns can improve separations and enable complex samples to be analysed. This Primer introduces comprehensive 2D chromatography, including instrument setups for different applications.