Formatted Title
Application of Nontargeted Analysis (NTA) via High-Resolution Mass Spectrometry (HRMS) for Identifying Transformation Products (TPs) during Hydrothermal Alkaline Treatment (HALT) of Per- and Polyfluoroalkyl Substances (PFAS)
Background/Objectives
Non-targeted analysis (NTA) via liquid chromatography-high resolution mass spectrometry (LC-HRMS) has increasingly become a powerful tool for identifying novel PFAS in the environment. While it has been applied to identify transformation products (TPs) formed by natural processes, very few studies report on applying NTA for identifying TPs during PFAS treatment applications, including the emerging hydrothermal alkaline treatment (HALT) technology, which has recently been reported to effectively degrade and defluorinate a wide range of PFAS detected in environmental matrices (e.g., aqueous film forming foam [AFFF]-impacted groundwater). The identification of TPs during HALT of individual PFAS including different chain lengths of perfluoroalkyl acids (PFAAs) will greatly assist our understanding of the controlling reaction mechanisms and close the carbon and fluorine mass balances.
Approach/Activities
Samples from HALT of individual PFAAs, including ultrashort and long-chain perfluoroalkyl carboxylates and sulfonates, were collected for analysis at different reaction conditions (reaction temperature, reaction time, and alkali concentrations). The samples were analyzed by Liquid Chromatography-Orbitrap High-resolution Mass spectrometry (LC–Orbitrap HRMS, Thermo-Fisher, Exploris 240) with a full MS/dd-MS2 scan mode. The acquired HRMS data were processed in Compound Discoverer 3.3 with a workflow developed by Thermo-Fisher and Colorado School of Mines. The identified fluorinated and non-fluorinated TPs were used for elucidating HALT reaction mechanisms. To test the effectiveness of this NTA workflow for a real-world PFAS sample, samples from HALT of foam fractionation (FF)-derived PFAS concentrate were analyzed as well.
Results/Lessons Learned
NTA results of HALT of individual PFAAs via LC–Orbitrap HRMS will help verify the nucleophilic substitution mechanisms previously proposed and help close the carbon and fluorine mass balance. The NTA analysis of HALT of FF-derived PFAS concentrate also revealed a range of non-fluorinated organic molecules that were recalcitrant. Future application of this NTA workflow on identifying TPs from other destructive treatment technologies (e.g., UV/Suflite) will also be discussed.