Special Considerations for MAS of Quadrupolar Nuclei

Quantification of MAS NMR spectra of quadrupolar nuclei posed many problems 10-15 years ago, with a number of Al NMR studies on both crystalline and glassy powders noting that the integrated signal intensity failed to agree both with the known 

Total relative intensity contributed to the centreband from all transitions 0.78 1.12 

Corrected centreband intensity to give the actual site distribution 1.28 0.89 

The advantages of fast spinning and high fields are also apparent in other materials. The observed signal of Al MAS NMR spectra of certain zeolites increased from 65 to 95% of that expected from the aluminium content when the magnetic field was increased from 9.4 to 18.8 T it should also be noted that these were samples in which the maximum Xq was only 6.3 MHz (Fyfe et al. 2001). 

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