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.