Comparison of on-line two-dimensional liquid chromatography modes for the analysis of organic micropollutants in wastewater treatment plant effluents.

The analysis of organic micropollutants (OMPs) in complex environmental samples such as wastewater using liquid chromatography coupled to mass spectrometry (LC-MS), is challenging due to the large number of known and unknown compounds, with very diverse chemical and physical properties. Two-dimensional liquid chromatography (2D-LC) coupled to high-resolution mass spectrometry (HR-MS) has emerged as an interesting alternative to address these challenges, but examples of applications remain limited. In this study, various 2D-LC modes, namely heartcutting (LC-LC), selective comprehensive (sLC × LC) and full comprehensive (LC × LC) 2D-LC, were investigated for the analysis of OMPs in the effluents of wastewater treatment plants (WWTPs) at three different locations in Flanders (urban, suburban, and rural). The highest effective peak capacities were obtained for a full comprehensive RPLC × RPLC method (np= 1525), followed by HILIC × RPLC (np= 1082), selective comprehensive sHILIC × RPLC (np= 519), and heartcutting HILIC-RPLC (np= 372), all outperforming one-dimensional (1D) RPLC (np= 370) and HILIC (np= 244) methods, which are currently the standard in environmental (OMP) analysis. The higher peak capacities for the 2D-LC methods were associated with a larger number of OMPs identified in the different WWTP-effluent samples, because of reduced peak overlap, and therefore lower matrix effects (ion suppression due to coelutions), despite the lower peak intensities of the 2D-LC methods. Important differences in OMP composition in effluents from different locations were observed, which is important for the ecotoxicological consequences on the receiving water bodies and for regulatory decisions on the management and implementation of new treatment technologies in different WWTPs. Finally, the 2D-LC methods, and especially RPLC × RPLC, showed great potential for future untargeted analysis and OMP quantification due to reduced matrix effects. Overall, 2D-LC, and especially RPLC × RPLC, was shown to be highly capable of separating complex OMP mixtures in WWTP-effluent samples, outperforming the conventionally used 1D-RPLC and 1D-HILIC methods.