Measurement of convection and temperature profiles in liquid samples

This paper describes a method for measuring the rate of convective how in a liquid sample used for high-resolution NMR. The measurement is straightforward and achieves a clean separation of convection from other effects such as diffusion and relaxation. Convection results from temperature gradients within the sample, and it is shown how these can be measured with the aid of a simple chemical shift imaging experiment of a sample whose spectrum shows a strong and well characterized temperature dependence. The use of these two methods is illustrated by showing how the rate of convection and the temperature profile depend on the solvent, temperature, and gas flow rate of the temperature regulating system. It is also shown that broadband C-13 decoupling results in significant temperature gradients and associated convection. (C) 1999 Academic Press.