A High‐Pressure NMR Probe for Aqueous Geochemistry

Abstract

A non-magnetic piston-cylinder pressure cell is presented for solution-state NMR spectroscopy at geochemical pressures. The probe has been calibrated up to 20 kbar using in situ ruby fluorescence and allows for the measurement of pressure dependencies of a wide variety of NMR-active nuclei with as little as 10 μL of sample in a microcoil. Initial (11)B NMR spectroscopy of the H3BO3-catechol equilibria reveals a large pressure-driven exchange rate and a negative pressure-dependent activation volume, reflecting increased solvation and electrostriction upon boron-catecholate formation. The inexpensive probe design doubles the current pressure range available for solution NMR spectroscopy and is particularly important to advance the field of aqueous geochemistry.

2H and 139La NMR Spectroscopy in Aqueous Solutions at Geochemical Pressures

“…H 2 Oa nd La(ClO 4 ) 3 + 2 H 2 Os olutions were determined as afunction of pressure in order to demonstrate anew NMR probe designed for solution spectroscopyatgeochemical pressures.T he 2 Hl ongitudinal relaxation rates (T 1 )v ary linearly to 1.6 GPa, consistent with previous work at lower pressures.T he 139 La T 1 values vary both with solution chemistry and pressure,but converge with pressure,suggesting that the combined effects of increased viscosity and enhanced rates of ligand exchange control relaxation. This simple NMR probe design allows experiments on aqueous solutions to pressures corresponding roughly to those at the base of the Earths continental crust.…”

“…[15] Changes in viscosity with pressure exert the dominant controls on relaxation. The T 1 values for 2 Hi n various LaCl 3 solutions vary by roughly af actor of 2-3 as af unction of electrolyte concentration (Figure 1b) Figure S4 in the Supporting Information) is constant to within 10 %a tP > 0.6 GPa indicating that the 139 La NMR relaxation is well correlated with 2 Hr elaxation at higher …”

High-pressure NMR spectroscopy in studies of the conformational composition of small molecules in supercritical carbon dioxide

“…On the other hand, lately, home-built probe head are significantly modernized and give good results in comparison with the first versions of the autoclave type probe head. For example, there is a specialized highpressure liquids probe head developed by William Casey's group at UC Davis [46] and the high-pressure MAS NMR probe heads/rotors developed at Pacific Northwest National Laboratory by Eric Walter and David Hoyt [47]. Thus, an alternative solution was chosen for obtaining NMR spectra under high pressure: special high-pressure tubes were used in combination with standard probe heads, without the need to modify their construction.…”

NMR spectroscopy of some electrolyte solutions to 1.9 GPa

“…Recently the HKF model was extended to 6.0 GPa and 1200°C via molecular-dynamic estimates of the dielectric constant of water (Pan et al, 2013;Sverjensky et al, 2014). These new pressure and temperature limits inspired the design of a nuclear magnetic resonance (NMR) probe for examining solute speciation at higher pressures (Pautler et al, 2014;Ochoa et al, 2015).…”