Formatted Title
An Innovative High-Resolution Parent Ion Search (HRPIS) Method to Selectively Identify Per- and Polyfluoroalkyl Substances
Background/Objectives
This study presents a time-of-flight mass spectrometry approach based on continuously interleaving scans at low and high collision energies (ToF-MSE) for the rapid identification and characterization of unknown per- and polyfluoroalkyl substances (PFAS). The MSE mode allowed for the simultaneous acquisition of full-spectrum accurate mass data of both parent and fragment ions in a single chromatographic run. We present a new identification approach for PFAS based on HR parent (precursor) ion search (PIS) experiments carried out on a ToF-MS system with MSE. PIS has been used previously in a triple quadrupole MS system (QqQ-MS) for the detection of novel chlorinated and brominated disinfection byproducts with the relative abundance ratio of chlorine or bromine isotopes as a diagnostic tool. However, fluorine has only one stable isotope (19F). We hypothesize that PFAS can be selectively detected by the ToF–MSE high-resolution parent-ion search (HRPIS) of their characteristic fragments. This hypothesis was confirmed with certified standards of PFAS, and our HRPIS method was applied to a group of PFAS-containing commercial samples, leading to the identification of 90 new PFAS. In this presentation, we will also showcase the application of this method in other projects.
Approach/Activities
The identification methodology of previously unknown PFAS was developed in two major steps. For the first step, HRPIS was performed on PFAS characteristic fragments to identify candidate PFAS parent ions from UPLC–ESI-ToF–MSE chromatograms. For the second step, the product-ion scan spectra of these candidate PFAS ions were studied, and possible formulas were proposed by the authors and then by the built-in software with a mass error tolerance of 20 ppm. The product ions and formulas were further investigated by authors to propose the structure of a candidate PFAS parent compound. An example of this non-targeted identification strategy has been provided in the Results and Discussion section. The accuracy of HRPIS was evaluated by the difference (error) between the measured mass and the calculated exact mass.
Results/Lessons Learned
We present HRPIS as a new non-targeted PFAS identification method. This method is transparent, readily transferable to other laboratories with similar instruments. To improve the selectivity, dual or multiple HRPISs of characteristic fragments are recommended. This approach was first validated by certified standards of PFAS in 10 different classes, and then applied to Fluorad brand surfactants used for consumer products. We identified 47 new poly-PFAS (40 neutrals, five zwitterions, two cations) and two novel classes of polyfluoroalkyl substances (or precursor compounds). The identification of 40 new non-ionic poly-PFAS in the present study expands the database of emerging PFAS. Ongoing experiments are underway to extend this approach to other matrixes and to investigate the fate, transport, and transformation of these newly identified compounds.