Enhancing the Separation and Quantification of Perfluoroalkyl Substances Using Polymeric Ionic Liquid Sorbents in Thin Film Microextraction

Abstract

The preconcentration and isolation of per- and polyfluoroalkyl substances (PFAS) remain challenging due to their varying chain lengths and diverse headgroup chemical functionalities. These substances are persistent and occur in the environment at low parts-per-trillion concentration levels, necessitating the use of efficient and selective sorbents that can enhance their preconcentration from the targeted sample prior to instrumental analysis. This study, for the first time, evaluates the use of a polymeric ionic liquid (PIL) consisting of 1-(9-carboxy-nonyl)-3-vinylimidazolium bromide [C₉COOHVim⁺] [Br^–] ionic liquid (IL) monomer and 1,12-di(3-vinylimidazolium)dodecane bromide ([C₁₂(Vim⁺)₂]2[Br^–]) IL cross-linker for the simultaneous separation and preconcentration of 15 anionic PFAS. The PIL was immobilized on a thin film microextraction device to improve preconcentration, extraction, and desorption kinetics. The addition of competing anions to the desorption solution was critical to ensure the quantitative desorption of the anionic PFAS by an ion exchange mechanism. Partition coefficient calculations revealed a balanced extraction coverage for short- and long-chain PFAS in ultrapure water, while in solutions at high ionic strength, short-chain PFAS tend to display less affinity for the sorbent compared to long-chain PFAS. Kinetic studies showed that less hydrophobic PFAS (perfluorobutanoic acid (PFBA)–perfluorohexanoic acid (PFHxA)) reached equilibrium faster and the extraction followed a pseudo-second order model with r² values up to 0.9874. The applicability of the PIL-thin film microextraction (TFME) device for quantitative analysis was demonstrated by a calibration curve in a concentration range from 1 ng L^–1 to 2500 ng L^–1, which showed good accuracy (70–130%), precision (<20%), and limits of quantification from 1 ng L^–1 to 50 ng L^–1.