Background Suppression in MAS-NMR

摘要

We report the use of pulse sequences for suppressing background signals fromspinning modules used in magic angle spinning (MAS) NMR. These pulses sequences are based on spatially selective composite 90 deg pulses originally reported by Bax, which provide for no net excitation of spins outside the homogeneous region of the coil. We have achieved essentially complete suppression of background signals originating from our Vespel spinning modules (which uses a free-standing coil) in both 1H and 13C spectra without noticeable loss in signal intensity. Successful modification of both Bloch decay and cross-polarization pulse sequences to include spatially-selective pulses was essential in acquiring background free spectra for weak samples. Background suppression was also found to be particularly valuable for both T1 and T1p relaxation measurements.