Radiation damping with water

Fig. 7. (A) The WEFT sequence in this sequence the tt pulse is applied to rotate all of the magnetization (i.e. both solute and solvent) to the -z-axis. A delay (I>np) of sufficient length is used to allow the water magnetization to relax to the origin ( >np = InfZ) ) whilst during the same period, by virtue of faster longitudinal relaxation, the solute resonances have reached thermal equilibrium. An excitation pulse (represented here as a tj/2 pulse) is then applied and an almost water-free spectrum is acquired. However, in the presence of radiation damping the water quicldy returns nonexponentially to the equilibrium position at a similar rate to the solute nuclei (see Fig. 2). However, if during D p a series of n very weak and evenly spaced gradient pulses are applied so as to inhibit the effects of radiation damping, the water relaxes according to its natural spin-lattice relaxation rate. This is the basis of the Water-PRESS sequence (B). An example of a spectrum obtained with Water-PRESS is shown in Fig. IB and Fig. 6.

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