Multidimensional chromatography in environmental analysis: Comprehensive two-dimensional liquid versus gas chromatography

Analysis of complex environmental matrices poses an extreme challenge for analytical chemists due to the vast number of known and unknown compounds, with very diverse chemical and physical properties. The need for a holistic characterisation of this complexity has sparked the development of effective tools to unravel the chemical composition of such environmental samples. Multidimensional chromatographic methods, namely comprehensive two-dimensional (2D) gas and liquid chromatography (GC × GC and LC × LC, respectively), coupled to different detection systems have emerged as powerful tools with the capability to address this challenge. While GC × GC has steadily gained popularity in environmental analysis, LC × LC is surprisingly less attractive in this research field. This critical review article explores the potential reasons why LC × LC is not the dominant technique used in environmental analysis as compared to GC × GC, while simultaneously highlighting the quite unique role of LC × LC for the target and untargeted analysis of complex environmental matrices. The possible combinations of stationary phases, the important role of the interfacing valve as the heart of an LC × LC assembly, the existing optimization strategies for improving the separation power in the 2D chromatographic space, and the need for user-friendly mathematical tools for multidimensional data handling are also discussed. Finally, a set of practical measures are suggested to increase the use and secure the success of LC × LC in environmental analysis.