Aqueous geochemistry could be extended considerably if nuclear-magnetic resonance (NMR) methods could be adapted to study solutions at elevated temperatures and pressures. We therefore designed an NMR probe that can be used to study aqueous solutions at gigapascal pressures. Fluoride solutions were chosen for study because 19 F couples to other nuclei in the solutions (31 P and 11 B) in ways that make peak assignments unequivocal. Correspondingly, NMR spectra of 19 F-and 11 B were collected on aqueous HBF 4-NH 4 PF 6 solutions to pressures up to 2.0 GPa. At pressure, peaks in the 19 F spectra were clear and assignable to the BF 4 À (aq), F À (aq) and BF 3 OH À (aq) ions, and these aqueous complexes varied in signal intensity with pressure and time, for each solution. Peaks in the 11 B spectra at pressure could be assigned to the BF 4 À (aq) and BF 3 OH À (aq) species. Additionally, there is a single peak that is assignable to H 3 BO 3 o (aq) and B(OH) 4 À (aq) in rapid-exchange equilibria. These peaks broaden and move with pressure in ways that suggest reversible interconversion of borate and fluoroborate species. The PF 6 À ion was found to provide a suitable 19 F shift and intensity standard for high-pressure spectra because it was chemically inert. The positions and intensities of the doublet peak also remains constant as a function of pressure and pH. Addition of electrolytes considerably distorts the phase diagram of water such that the stability region of the aqueous solution expands to well beyond the 0.8 GPa freezing pressure of pure water; some fluoroborate solutions remain liquid until almost 2.0 GPa.

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High pressure assisted infusion of nutrients into food was in situ monitored with magnetic resonance imaging (MRI). Modification of an off-the-shelf pressure reactor with an MRI detection circuit provided a large enough volume to accommodate food. The model food used here was peeled apple flesh as it is considered as a good mimic for fibrous food. The nuclear spin relaxation properties of the water surrounding the apple flesh were enhanced by adding paramagnetic manganese cations. In this way, MRI relaxation contrast can be used to monitor the location of doped bulk water in and around the apple flesh during pressurization. This work tracked the efficiency of pressure induced nutrient infusion in situ, demonstrating that pressure gating and ramping offer no nutrient mass transport advantage over operation at constant pressure and that the presence of a peel expectedly disrupts solute transport into the fruit. High pressure assisted infusion, with all pressurization strategies shown here, yielded nearly 100-fold faster infusion times than at ambient pressure.

Aminopolymer-based adsorbents are commonly investigated for CO2 direct air capture (DAC). In the presence of high temperature and O2, which could happen during process upset, oxidative degradation can significantly contribute to limiting the adsorbent lifetime. Here, we demonstrate the use of a portable, benchtop NMR sensor to collect proton relaxometry profiles to track the degradation of a PEI/Al2O3 sample exposed to controlled accelerated oxidation conditions and correlate the extent of oxidation as measured by loss in amine efficiency with T2 (spin-spin) relaxation times. We hypothesize that T2 relaxation accurately tracks oxidative degradation in aminopolymers because of reduced polymer mobility resulting from radical-induced crosslinking that can occur during the oxidation process. The advantage of using NMR relaxometry as a non-destructive technique to probe degradation is demonstrated on a 1-inch square-channel monolith adsorbent exposed to actual DAC service conditions, highlighting the potential for using this technique as a rapid and non-destructive method of probing adsorbent health.