Sealing effect of magic-angle-spinning rotors in solid-state NMR.

Several methods are proposed to check the sealing of a magic-angle-spinning (MAS) rotor. The intrusion of moisture into the MAS rotor is checked by trimethylphosphine oxide, which is highly hygroscopic. Its hydrated form is separately observed in (31)P MAS NMR spectra from the crystalline (anhydrous) form. (1)H MAS NMR can monitor the hydrated form, the crystalline form, and adsorbed water independently. Gas leakage from the MAS rotor is monitored by measuring (129)Xe MAS NMR spectra of xenon (Xe) confined in zeolites as well as (3)He MAS NMR spectra of (3)He gas. The sealing effect of MAS rotors has been checked quantitatively using the above methods.