Quantitative Measurement of TFA and Other Short Chain PFAS in Environmental Samples Using ¹⁹F SSFP-CRAFT NMR

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Nuclear Magnetic Resonance (NMR) is often perceived as having limited sensitivity for complex sample analysis.
• Fluorine NMR (¹⁹F NMR) has shown promise for analyzing per- and polyfluorinated alkyl substances (PFAS).
• Quantitative analysis of ultrashort chain PFAS, like trifluoroacetic acid (TFA), is crucial for understanding environmental contamination.

Purpose of the Study:

• To adapt and validate the steady-state free precession (SSFP) NMR with complete reduction to amplitude frequency tables (CRAFT) method for quantitative analysis of ultrashort chain PFAS.
• To assess the sensitivity and quantitation capabilities of the adapted ¹⁹F SSFP-CRAFT NMR method.
• To measure TFA and other PFAS concentrations in diverse real-world environmental and biological samples.

Main Methods:

• Adaptation of the SSFP-NMR technique combined with CRAFT data analysis for quantitative ¹⁹F NMR.
• Implementation of rapid radiofrequency pulses to achieve high scan counts and improve sensitivity.
• Application of the quantitative method to analyze drinking water, Arctic surface waters, human serum, and plant samples.

Main Results:

• The SSFP-CRAFT method achieved instrument detection limits as low as 0.16 μg L^-1 TFA in aqueous samples under quantitative conditions.
• Trifluoroacetic acid (TFA) was detected and quantified in all tested real-world samples.
• High concentrations of TFA were found in spinach leaves (1540 ng g^-1), potentially explaining elevated levels in human serum (19.5 ng mL^-1).

Conclusions:

• The quantitative ¹⁹F SSFP-CRAFT NMR method overcomes the traditional sensitivity limitations of NMR for PFAS analysis.
• This method provides a powerful tool for accurate quantification of TFA and other PFAS in complex environmental and biological matrices.
• Findings suggest plant uptake of TFA may contribute to human exposure and elevated serum concentrations.