Lock signal heteronuclear

If the intensity of the desired signal is the limiting factor, then phase cycle selection is preferred. A phase cycle selection version of HMQC that uses a spin-lock to purge signals from molecules containing NMR silent 5 nuclei has been developed—poor man s gradient-heteronuclear... 

To summarize the experiment, one applies a r/2 pulse to H, which is followed by a change of 90° in the phase of the RF field of relative to the first pulse. This leads to the spin-locking of the abundant spin system. Still under the spin-locking condition, which was used to lower the spin temperature [4] much below the lattice temperature, the Hartmann-Hahn condition is established, and this situation is kept until the polarization transfer from H to spins is complete. After that, the observation of the FID is performed under heteronuclear decoupling. In order to increase the signal-to-noise ratio of FID, the CP-MAS experiment is repeated as many times as necessary, just waiting the time necessary for the total H spin-lattice relaxation between acquisitions. MAS is continuously applied during the experiment. 

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