Deuterium nuclear magnetic resonance spin-lattice relaxation of analytically relevant solvent systems

We previously reported that the nuclear magnetic resonance (NMR) 14N spin-lattice relaxation times (T1) of CH3CN in CH3CN-H2O mixtures directly correlate with the solution viscosity when scaled for temperature (eta/T) in this common chromatographic mobile phase system.' Here, we demonstrate that the 2HT1 relaxation times also correlate with viscosity, contrary to a previous report. (2) This establishes 2HT1 relaxation times as a useful means of measuring changes in solution viscosity in CH3CN-H2O mixtures. We show thermal convection to result in grossly decreased, apparent T1's, by as much as approximately 40%, in nonspinning samples. This effect can be eliminated by moderate sample rotation or confinement of the sample to within the rf-irradiated region. The problem of thermal convection is revealed in systems having long Ti's and has implications in T1 experiments employing nonspinning samples at elevated temperatures, including inherently nonspinning systems, such as those used in high-pressure studies.