Deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy is a useful tool in probing molecular association between components in a binary hydro-organic mixture, such as tetrahydrofuran (THF) and water. Measurements of (2)H longitudinal relaxation times (T(1)) for deuterated analogs of THF and water provide this type of information, since the magnitude of T(1) is indicative of molecular association and mobility. This technique is also useful in determining the interactions between the mobile phase and reversed-phase stationary phase. T(1) measurements of slurry samples, consisting of both mobile- and stationary-phase components, allow for changes in the longitudinal relaxation time of mobile-phase components upon contact with the stationary phase (ΔT(1)) to be monitored. These ΔT(1) values are indicative of the degree of association of the THF-water mobile-phase components with the stationary phase.