PFG NMR diffusion experiments for complex systems

Abstract

Many practical applications of diffusion NMR, ranging from biomedical to industrial, entail the measurement of low-concentration solutes in non-deuterated, compositionally complex systems. The aim of this article is to present examples of robust, versatile diffusion experiments that can be used with non-deuterated solvents and at non-ambient temperatures. Specifically, three experiments are presented in detail: CONVEX, which combines excitation-sculpting solvent suppression with double-echo convection-compensating PGSE; DQDiff, which implements double-quantum filtered diffusion measurements in a convection-compensating mode; and applications of Oscillating-Gradient Spin-Echo (OGSE) to systems with homonuclear scalar couplings. These examples are based on the recent work by the authors and relate to a variety of systems, ranging from simple solutions to colloidal and polymeric systems. Besides the applied aspects, we review the general methodology used to treat the effects of diffusion and flow in NMR experiments, and apply this theory to derive the diffusion attenuation expression for each of the experiments presented. The paper should be useful to beginners as well as advanced users of general NMR wishing to learn about diffusion measurements.