Multiple Quantum Magic-Angle Spinning (MQ-MAS) is a solid-state NMR method for obtaining a high resolution spectrum of half-integer spin quadrupolar nuclei. It was invented by Professor Lucio Frydman and coworkers. It is performed as a two-dimensional NMR experiment, and correlates a high resolution (isotropic) spectrum to the anisotropic central transition MAS spectrum. Below are the two most basic MQ-MAS sequences.
To determine when the MQ-MAS echo occurs in t2 consult the table below:
For additional implementation details (phase cycling and data processing), please see the references below, particularly, Massiot et al. Solid-State NMR, 6, 73 (1996).