Repetitive sideband-selective double frequency sweeps for sensitivity enhancement of MAS NMR of half-integer quadrupolar nuclei

• Published in: Journal of magnetic resonance (1997) Vol. 219; pp. 25 - 32
• Main Authors: Goswami, M., van Bentum, P.J.M., Kentgens, A.P.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-06-2012
• Subjects: Adiabatic pulse; Albite; Algorithms; Computer Simulation; Distortion; Double frequency sweeps; Joining; Magnetic fields; Magnetic Resonance Spectroscopy; MAS; Models, Chemical; Quadrupolar nuclei; Sensitivity and Specificity; Sensitivity enhancement; Signal to noise ratio; Spectra; Spin-lattice relaxation; Spinning; Zoisite; Double frequency sweeps; CT; ST; Zoisite; Adiabatic pulse; Quadrupolar nuclei; Albite; Sensitivity enhancement; MAS
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2012.04.007

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► An improved double frequency sweep for enhancing quadrupolar NMR spectra. ► Adiabatic inversion of the satellite transition sidebands under magic angle spinning. ► Enhancements of ∼3 are achieved by applying this sideband selective DFS to 27Al . ► Repetitive application of the ssDFS leads to sensitivity enhancements of up to 5. ► Spectral editing by selectively enhancing one of the quadrupolar sites using ssDFS.
A sensitivity enhancement scheme aiming at selective adiabatic inversion of a single set of satellite transition sidebands under magic angle spinning has been employed on samples of albite containing a single moderately distorted 27Al site and zoisite containing two highly distorted octahedral 27Al sites. Overall enhancements of ∼2.5 for albite and ∼3 for the two AlO6 sites of zoisite are reported by applying this scheme at different spinning speeds reflecting the versatility of this enhancement scheme which achieves significant signal-to-noise enhancements for the systems with moderately high quadrupolar coupling and high quadrupolar coupling. Repeating the sensitivity enhancement scheme and signal readout several times without allowing for spin-lattice relaxation leads to sensitivity enhancements of factors of ∼4 for albite and ∼5 for zoisite which substantially increases the detectability of the quadrupolar sites. The effectiveness of this scheme at high magnetic field under very fast magic angle spinning has been demonstrated. Finally, the possibility of performing spectral editing by selective enhancement of one of the quadrupolar sites in zoisite whilst keeping the other site unaffected has been explored.