Cyclical Electrical Field-Flow Fractionation for Retention Characterization of Per- and Polyfluoroalkyl Substances

Abstract

Per- and polyfluoroalkyl substances (PFAS) are environmentally persistent contaminants that are difficult to monitor and separate because of their chemical stability and diverse physicochemical properties. In this study, the retention behavior of several PFAS, including perfluorooctane sulfonate, perfluorohexane sulfonate (PFHxS-K), perfluorobutanesulfonate (PFBS), hexafluoropropylene oxide dimer acid, and perfluorononanoic acid, was investigated using Cyclical Electrical Field-Flow Fractionation (CyElFFF). The selected compounds represent PFAS with different chain lengths, functional groups, and environmental relevance. Field-off injections established the void response, while application of a cyclical electric field produced analyte-dependent retained peaks, demonstrating that CyElFFF can induce measurable retention for multiple PFAS compounds. Voltage and frequency sweeps showed that retention behavior is sensitive to the applied electrical conditions, with increasing voltage generally increasing retention and frequency changes producing smaller but measurable changes in peak position and shape. PFBS concentration studies showed that increasing concentration primarily increased peak height, while retention ratios and peak positions changed only slightly over the tested range. The PFBS/PFHxS-K mixture was not baseline-resolved under the tested conditions. Because the mixture and individual standards were not matched for total PFAS concentration, conductivity, or ionic strength, the cause of the shifted mixed-sample response could not be determined. In addition, conductivity detection could not specifically identify the contribution of each compound to the mixed profile. Overall, these results show that CyElFFF can induce and modulate retention for multiple PFAS, while baseline mixture separation will require further optimization of operating conditions and reduction of non-ideal channel interactions. Experiments were carried out at part-per-million concentrations to establish fundamental transport behavior rather than to demonstrate trace-level detection.