Non-targeted analysis of organic acids in water by strong anion exchange SPE and mixed-mode LC-HRMS Davide Ciccarelli 1,3 , Paolo Vineis 2,3 , Tim Marczylo 3,4 , Leon Barron 1,3 1 Environmental Research Group, MRC Centre for Environment and Health, UK, 2 Department of Epidemiology and Biostatistics, School of Public Health, UK, 3 NIHR-HPRU Chemical and Radiation Threats and Hazards, UK, 4 UK Health Security Agency, Harwell Science Campus, UK Non-Targeted Analysis (NTA) in water aims theoretically at detecting all substances contained in a sample. The scientific community is placing an increasing attention on the importance of extending the scope of sample preparation and/or chromatographic methods to very polar compounds. The vast majority of published NTA methods for water samples employ a single extract in which all sample components are concentrated. However, co-elution during liquid chromatography-electrospray ionization-mass spectrometry analysis generates competition for the sites on the charged surface of the droplets, leading to signal suppression. Furthermore, co-elution increases the complexity of full-scan and data-dependently acquired spectra, ultimately affecting their deconvolution. This poster presents a selective sample fractionation approach to decrease extract complexity and minimise co-elution. Using solid-phase extraction (SPE) and a mixed-mode anion exchange-reversed-phase chromatographic column to help provide this selectivity, a selection of 24 highly toxic acidic substances were used to develop a suitable qualitative analytical method for application to drinking water. These included perfluoroalkyl acids, herbicides, disinfectant by-products, selected metabolites of halogenated flame retardants and industrial reagents. With a 100-fold concentration factor and with average recoveries of 87 % on a silica-based strong anion exchange SPE resin, low-mid ng/L concentration level sensitivity was achieved for all compounds and to within 5 ppm mass inaccuracy. The data processing workflow for wider application to NTA was tailored to exclude features generated by sample preparation, instrument and dissolved organic matter, minimising the risk of false positives and the workload for the analyst. The developed method was then applied to suspect screening and NTA of highly toxic substances in several samples of UK municipal drinking water. In many cases, clear peaks were attributable to target substances used during method development as well as additional acidic contaminants. Overall, this method represents an efficient meansto recover, detect and identify anionic species at very low concentrations in water matrices in comparison to existing qualitative methods.
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