Facile identification of fluorosurfactant category in aqueous film-forming foam concentrates via optimized 19F NMR

Abstract

Aqueous film-forming foams (AFFFs) are the primary source of toxic perfluoroalkyl and polyfluoroalkyl substances (PFAS) in wastewater. Thus, it is urgent to develop a facile and fast method for identifying fluorosurfactants in commercially available AFFFs. In this work, fluorine nuclear magnetic resonance (¹⁹F NMR) spectroscopy was optimized to measure AFFFs directly with the extra addition of 5% D₂O as the locking reagent, and high-quality spectra could be acquired within 4 min (0.1% fluorosurfactant content). Recovery experiments demonstrated that the use of different AFFFs had no marked influence on the quantitative analysis of fluorosurfactants. Such method works with low-field NMR spectroscopy (1.4 T) as well. Two-dimensional (2D) ¹⁹F COSY NMR was used to make signal assignments for different fluorosurfactant derivatives. The optimized ¹⁹F NMR could quantify the commercially available fluorosurfactants in different AFFFs, identify them being in either the perfluorooctane sulfonate (PFOS) or fluorotelomer sulfonic acid (FTS) categories, and distinguish the head-group of PFOS and FTS derivatives, which exhibits great potentials in the developments of relevant commercial detections.