Improving the sensitivity of MAS spheres using a 9.5 mm spherical shell with 219 μL sample volume spinning in a spherical solenoid coil
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Date
2022-10
Publication Type
Journal Article
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yes
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Abstract
Spherical rotors in magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments have potential advantages relative to cylindrical rotors in terms of ease of fabrication, low risk of rotor crash, easy sample exchange, and better microwave access. However, one major disadvantage so far of spherical rotors is poor NMR filling factor due to the small sample volume and large cylindrical radiofrequency (RF) coil. Here we present a novel NMR coil geometry in the form of a spherical coil. The spherical coil best fits the spherical sample to maximize sensitivity, while also providing excellent RF homogeneity. We further improve NMR sensitivity by employing a spherical shell as the rotor, thereby maximizing sample volume (219 μL in this case of 9.5 mm outer diameter spheres). The spinning gas is supplied by a 3D-printed ring stator external to the coil, thereby introducing a simplified form of MAS stators. In this apparatus, the RF field generated along the coil axis is perpendicular to the external magnetic field, regardless of rotor orientation. We observe a linear increase in sensitivity with increasing sample volume. We also simulate the RF performance of spherical and cylindrical solenoid coils with constant or variable pitch for spherical and cylindrical rotors, respectively. The simulation results show that spherical solenoid coils generate comparable B1 field intensities but have better homogeneity than cylindrical solenoid coils do.
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published
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Journal / series
Volume
343
Pages / Article No.
107305
Publisher
Elsevier
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Edition / version
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Software
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Date collected
Date created
Subject
NMR filling factor; Magic angle spinning; Radiofrequency coil; NMR sensitivity; Spherical rotor; Spherical solenoid coil; Variable-pitch solenoid coil
Organisational unit
02515 - Laboratorium für Physikalische Chemie / Laboratory of Physical Chemistry
Notes
Funding
201070 - Dynamic Nuclear Polarization at Room Temperature for High Sensitivity Nuclear Magnetic Resonance (SNF)