Separation of components of a 1H NMR composite signal by nutation experiments under low amplitude radio-frequency fields. Application to the water signal in clays

NMR nutation experiment consists in probing the evolution of nuclear magnetization perpendicularly to a radio-frequency field applied for a variable time. It is shown theoretically and experimentally that, under weak radio-frequency field conditions, the nutation frequency depends on relaxation rates. The Fourier transform of the nutation curve, which is obtained by plotting the signal amplitude as a function of the rf field application time, yields separate bands corresponding to the components of the unresolved composite signal. This can be only achieved if these components possess different relaxation characteristics. This new method is applied to the study of water in clays.