Simultaneous Multinuclear Steady State Free Precession for Process Monitoring in Per- and Polyfluoroalkyl Substance Systems with Multi-Receive Nuclear Magnetic Resonance

Monitoring fast, complex processes by NMR requires excellent sensitivity and time resolution, while additional heteronuclear information helps provide greater insight into changes. Steady-state free precession (SSFP) maintains the magnetization in the steady-state, allowing 10−100’s of acquisitions per second, increasing NMR sensitivity albeit with a reduction in spectral resolution. This work presents simultaneous multinuclear (SIM)-SSFP, a multi-receive NMR experiment in which SSFP is performed on two nuclei simultaneously (1H and 19F here) to collect independent 1D datasets for process monitoring. The approach provides identical sensitivity and spectral resolution as traditional SSFP, effectively providing a second SSFP NMR spectrum “for free”. SIM-SSFP is first demonstrated in the oxidation of 3-trifluoromethyl-4-nitrophenol to highlight the value of multinuclear datasets in understanding reaction mechanisms and is subsequently applied to follow total oxidizable precursor (TOP) assays on 6:2 fluorotelomer alcohol and an aqueous film-forming foam (AFFF; a per- and polyfluoroalkyl substance (PFAS) mixture) to understand the reaction mechanisms. The NMR results indicated incomplete conversion of the unknown PFAS in the AFFF, while in all samples the TOP assays mineralized some of the organic fluorine to inorganic fluoride, which is challenging to measure by mass spectrometry, and could lead to the underestimation of PFAS contaminants. We suggest NMR is an excellent complementary approach to understand TOP assays and can support the development of improved methods for environmental analysis. In summary, SIM-SSFP allows SSFP acquisition on two nuclei simultaneously without compromising either dataset, and supports process monitoring in any sensitivity-limited application where information from multiple nuclei are required.