Observation and selective suppression of the dipolar-field effects in 2D NMR in liquids in homogeneous fields

Intense and numerous satellite peaks caused by the dipolar field have been observed in COSY experiments performed in homogeneous magnetic fields on a concentrated sample (proton NMR at 600 MHz on a dilute solution of acetone in water). Radiation damping was made negligible by the use of a very small sample. As shown by numerical simulations, these results are predicted in great detail by the simple, traditional theory based on Bloch equations incorporating relaxation and the classical average dipolar field caused by all spins in the sample. A simple and efficient decoupling scheme has also been demonstrated by which dipolar-field effects caused by a concentrated solvent can be suppressed for all peaks in the spectrum, except for a narrow spectral range around the NMR frequency of the solvent itself. This scheme should prove very useful for experiments in homogeneous fields as soon as radiation damping is routinely eliminated by the techniques which are presently under development. (C) 1996 Academic Press, Inc.