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

NMR has long been perceived to have relatively poor sensitivity vs other methods. However, NMR can be highly useful for examining complex samples. Fluorine NMR has been routinely demonstrated in the literature to be a powerful discovery tool in the analysis of per- and polyfluorinated alkyl substances (PFAS) in a variety of environmental and biological samples. In this study, we adapt the previously published steady-state free precession (SSFP) NMR with non-Fourier transform data analysis (complete reduction to amplitude frequency tables (CRAFT)) for quantitative analysis of ultrashort chain fluorinated acids. SSFP-CRAFT results have challenged the perception that NMR is sensitivity-limited but has not yet been shown to be fully quantitative. Adapting the SSFP-CRAFT approach for quantitative measurement of TFA, PFMeS, and other selected PFAS is a crucial step in further understanding environmental contamination from these species. Sensitivity is improved over conventional NMR using rapid radiofrequency pulses to collect hundreds of thousands of scans in short experiment times, allowing for instrument detection limits as low as 0.16 μg L^-1 TFA in aqueous samples under fully quantitative NMR conditions. The quantitative ¹⁹F SSFP-CRAFT NMR method is used to measure concentrations of TFA and other PFAS in four real world samples: drinking water, Arctic surface waters, human serum, and plants intended for human consumption. TFA was found and quantified in all samples. The very high concentration of TFA in the leaves of spinach (1540 ng g^-1) points to a potential exposure pathway partially explaining higher than expected TFA concentrations in human serum, at 19.5 ng mL^-1.