Characterizing a Mixed Mode Fluorocarbon/Weak Anion Exchange Sorbent for PFAS Separation

While per- and polyfluoroalkyl substances (PFAS) are widely used due to their high thermal and chemical stability, their pervasive presence and resistance to degrading have led researchers to seek effective methods for their detection and removal. A recent study spotlighted a new fluorinated weak anion exchange resin synthesized to increase selectivity for extraction of PFAS. The paper inspired by the research states that the polystyrene-divinylbenzene resin material developed, Sepra-WAX-KelF-PEI, has demonstrated the ability to provide balance coverage in efficiently capturing both short-chain and long-chain PFAS. LCGC International spoke to Emanuela Gionfriddo, corresponding author of the paper and a professor at the University at Buffalo, the State University of New York, about the resin and the work behind it.

In your paper (1), you detail the synthesis of a new fluorinated weak anion exchange resin to increase selectivity for extraction of PFAS. Why do you believe there was a need for this?

PFAS are ubiquitous chemicals that are currently highly targeted by regulatory agencies due to their bioaccumulation and potential adverse effects on humans and other organisms. Extraction and preconcentration of PFAS mixtures must be efficient and selective, especially in the presence of co-extractants in complex samples. Our previous work demonstrated that weak anion exchange sorbents are ideal sorbents for SPME of PFAS due to the ion exchange interaction with their charged headgroups (2,3). This new sorbent that adds fluorinated moieties to a weak anion exchange resin was synthesized at the laboratory of our collaborator, Neil D. Danielson of Miami University, and was designed to increase further the selectivity for PFAS through ion exchange and fluorine-specific interactions that target the fluorinated portion of PFAS molecules, thus enhancing sorbent selectivity.

Methods using sorbents for pre-concentration include solid-phase extraction (SPE) and solid-phase microextraction (SPME). Would you consider this method one of these techniques, or would you give it a different name?

No, the extraction devices created using these WAX-fluorinated sorbents follow the fundamental principles of SPME. In my opinion, renaming techniques based on minor modifications of geometries, sorbents or design of the devices creates unnecessary confusion, especially for younger scientists who are learning about extraction methods. The techniques should be named or classified based on the fundamental principles they abide by.

How were pre-concentrated samples introduced into the liquid chromatography-tandem mass spectrometry (LC–MS/MS) system? Were there special considerations or requirements for sample handling?

After preconcentration, the analytes were desorbed in a mix of solvents that guaranteed quantitative desorption of PFAS. To minimize carryover on the sorbent, salt additives were added to disrupt the electrostatic interaction between PFAS and the sorbent; these salts and their concentration in the desorption solution must be carefully selected to guarantee compatibility with LC-MS.

Briefly state your overall findings in this study.

We established that the addition of fluorinated moieties on the sorbent improved the extraction of hydrophobic PFAS by almost double compared to the non-fluorinated counterpart. On the other hand, ion exchange remained the predominant extraction mechanism for short-chain PFAS. Therefore, the addition of polyethyleneimine to the sorbent structure to increase its anion exchange capability proved to be crucial for the extraction of short-chain PFAS, with an increase in extraction efficiency up to tenfold.

What were the major challenges you encountered in your work?

The chemistry of these sorbents was very different than what was used in my laboratory before. The protocol for creating the SPME devices, therefore, had to be reoptimized to guarantee a smooth and reproducible immobilization of the sorbent onto the fiber support.

You’ve recently moved to the University at Buffalo (UB). How has that transition been so far?

The transition worked well, and the Department of Chemistry at UB has been, so far, an excellent platform for my group and me to continue and expand the reach of our research program. The Department has a strong tradition in analytical chemistry and separation science and promotes interdisciplinary research, which fits very well with the goals and aspirations of my laboratory.

Emanuela Gionfriddo, an associate professor of chemistry at the University at Buffalo. Photo courtesy of Emanuela Gionfriddo.

References

1. Olomukoro, A. A.; Xie, R.; Paucar, F. X. F.; DeRosa, C.; Danielson, N. D.; Gionfriddo, E. Characterization of a Mixed Mode Fluorocarbon/Weak Anion Exchange Sorbent for the Separation of Perfluoroalkyl Substances. J. Sep. Sci. 2024, 47 (16), e2400413. DOI: 10.1002/jssc.202400413

2. Olomukoro, A. A.; DeRosa, C.; Gionfriddo, E. Investigation of the Adsorption/Desorption Mechanism of Perfluoroalkyl Substances on HLB-WAX Extraction Phases for Microextraction. Anal. Chim. Acta 2023, 1260, 341206. DOI: 10.1016/j.aca.2023.341206

3. Olomukoro, A. A.; Emmons, E. V.; Godage, N. H.; Cudjoe, E.; Gionfriddo, E. Ion Exchange Solid Phase Microextraction Coupled to Liquid Chromatography/Laminar Flow Tandem Mass Spectrometry for the Determination of Perfluoroalkyl Substances in Water Samples. J. Chromatogr. A 2021, 1651, 46235. DOI: 10.1016/j.chroma.2021.462335