Quasi-targeted analysis of halogenated organic pollutants in fly ash, soil, ambient air and flue gas using gas chromatography-high resolution mass spectrometry with isotopologue distribution comparison and predicted retention time alignment

Identifying environmental pollutants, particularly emerging and new pollutants, in various matrices is a prerequisite for further research involving these pollutants. In this study, we developed a quasi-targeted analysis method to identify halogenated organic pollutants (HOPs) by joint application of gas chromatography-double focus magnetic-sector high resolution mass spectrometry (GC-DFS-HRMS), isotopologue distribution comparison and predicted retention time (PRT) alignment. Structures of a variety of unreported/scarcely reported HOPs were conceived and sketched, and then, multiple isotopologue ions of individual HOPs were detected by GC-DFS-HRMS in multiple ion detection mode. Comparisons between the detected mass spectra and the theoretically simulated isotopologue distributions were conducted via paired-samples T-test and cosine similarity analysis. PRT alignment was further applied to exclude interferences that presented unreasonable retention times. The method was validated with dozens of commercially available reference standards of conventional HOPs and several unintended byproducts comprising mix-chlorinated/brominated benzenes in some commercial halogenated-benzene standards, showing good reliability and accuracy. Application of the developed method was primarily implemented with fly ash from municipal solid waste incineration plants. In total, 106 molecular formulas corresponding to unknown or little-known HOPs were identified, of which many were mix-halogenated compounds. Six HOPs were structurally elucidated, including three sulfur-containing dioxin-like HOPs, two mix-perhalogenated benzenes, and a pentabrominated anisole. The structures of 18 compounds that individually contained 2-4 theoretical isomers were putatively elucidated according to the PRT alignment. In addition to fly ash, other environmental matrices, including soil, ambient air and flue gas, were screened by the method, and a number of HOPs were also found in these matrices. This method is feasible, reliable, accurate and sensitive for the identification and screening of potential unknown HOPs in the environment and should facilitate further research, such as pollution investigations and eco-environmental risk assessments for these pollutants.