Sensitivity enhancement of the MQMAS NMR experiment by fast amplitude modulation of the pulses

We report here an improved way of doing the multiple-quantum magic-angle spinning (MQMAS) NMR experiment that relies on the use of amplitude modulated pulses. These pulses were found to yield MQMAS NMR signals that are considerably stronger (≈200–300%) than the ones arising from the usual continuous wave pulse schemes by virtue of a superior efficiency of the triple- to single-quantum conversion process. Numerical simulations and experimental results taking 23Na and 87Rb nuclei as examples are presented that corroborate the usefulness of this approach.