MAS NMR with a spherical rotor in a 10 mm NMR tube

Abstract

Magic-angle spinning (MAS) partially averages anisotropic NMR interactions to improve spectral resolution of solid samples. MAS requires the sample to be spun precisely about an angle of 54.74° with respect to the magnetic field. This technique introduces components within MAS NMR radiofrequency probes that are distinguishable from their solution-state counterparts - most notably, a stator that spins and sets the angle of spinning axis. Here, we present an MAS stator that spins and pneumatically sets the spinning axis angle of a 6 mm spherical rotor (65µL sample volume) while inside a 10 mm solution-state NMR tube. ⁷⁹Br experiments are used to verify the pneumatic adjustment and stability of the spinning angle, with ⁷⁹Br spinning echoes from KBr observed out to 8 ms. Utility for solid state MAS NMR is then demonstrated by a ³¹P experiment of a proton-free inorganic phosphate, K₄P₂O₇. Although this stator is applied here as an MAS insert that expands the utility of a solution-state probe, its compact design is advantageous for any spinning experiments in a restricted space.