The use of sample rotation for minimizing convection effects in self-diffusion NMR measurements.

Abstract

Undesirable temperature gradients in a NMR sample tube are usually generated by an inappropriate temperature regulation system. We have shown that such convection effects can greatly distort the measurement of translational self-diffusion coefficients. The use of sample spinning helps to minimize such undesirable effects by disruption of convection fluxes due to resulting Coriolis forces that have a strongly stabilizing effect on the conducting state of the system (J. Lounila et al., J. Magn. Reson. A 118, 50 (1996)). This simple trick allows the accurate measurement of diffusion coefficients for a wide range of temperatures and solvents without the need for a convection-compensated NMR pulse sequences or more sophisticated temperature control units. Experimental data obtained for some target compounds dissolved in several common deuterated solvents at different temperatures are reported and discussed.