NMR spectroscopy of some electrolyte solutions to 1.9 GPa

Abstract Nuclear-magnetic resonance (NMR) spectra of CsCl and LaCl 3 in D 2 O/H 2 O solutions were collected up to pressures of 1.9 GPa using a new NMR probe design that considerably extends the pressure range available for geochemical experiments. The longitudinal-relaxation times ( T 1 ) for 2 H compare well with those reported in the previous studies of Lee et al. (1974), who examined lower pressures, and indicate that the probe functions properly. In some experiments, 133 Cs and 1 H NMR spectra could be taken on solutions to pressures well beyond the nominal freezing pressure of D 2 O or H 2 O to form Ice VI (near 0.9 GPa). Freezing to form the high-pressure ice is kinetically slow on an experimental time scale (minutes to hours). The data indicate that the electrolyte concentrations increase the freezing pressure of the solution. This result means that solution NMR spectra can be collected at pressures that are nearly twice the nominal freezing pressure of pure D 2 O or H 2 O. Pulsed-magnetic-field-gradient NMR methods are used to independently measure the self-diffusion coefficient of H 2 O in these solutions, which yields estimates of solution viscosity via the Stokes–Einstein relation. The increased viscosity accounts for the pressure variation of T 1 values as rates of molecular tumbling are affected. Accounting for such changes is essential if NMR spectral line widths are used to infer pressure-enhanced rates of geochemical reactions, such as interconversion of aqueous complexes.