Experimentally Determined Aqueous Diffusion Coefficients of PFAS Using ¹⁹F NMR Diffusion-Ordered Spectroscopy

Per- and polyfluorinated alkyl substances (PFAS) can be found in nearly every aqueous environmental compartment, including rainwater, snow, surface waters, lakes, and oceans. Despite the global distribution of PFAS in the aquatic environment, little is known regarding their diffusion through aqueous systems. This can be limiting for passive sampling techniques, which depend on accurate diffusion coefficients to relate sampler concentrations of PFAS to system-wide concentrations. Existing methods for the measurement of aqueous diffusivity can be time-consuming, challenging, and subject to error when measuring highly fluorinated surfactants. In the present study, we employ fluorine NMR diffusion-ordered spectroscopy (19F DOSY) to experimentally determine the aqueous diffusion coefficient accurately for 47 PFAS. Aqueous diffusion was found to decrease with increasing fluorinated chain length and increase with the inclusion of ether linkages. The impacts of the ionic strength, temperature, and concentration on the aqueous diffusion of PFAS were also examined. The 19F NMR DOSY method demonstrates reasonable agreement with literature values where available. Numerous PFAS do not have published aqueous diffusion coefficients, which are reported here for the first time. This data allow passive sampling and environmental modeling methods to be greatly improved for monitoring PFAS in the aquatic environment.