Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5407680 | Journal of Magnetic Resonance | 2006 | 8 Pages |
Abstract
The pursuit for more sensitive NMR probes culminated with development of the cryogenic cooled NMR probe. A key factor for the sensitivity is the overall resistance of RF circuitry and sample. Lowering the coil temperature to â¼25Â K and the use of superconducting coil material has greatly reduced the resistance contribution of the hardware. However, the resistance of a salty sample remains the same and evolves as the major factor determining the signal-to-noise ratio. Several approaches have been proposed to reduce the resistance contribution of the sample. These range from encapsulating proteins in a water cavity formed by reverse micelles in low viscosity fluids to the optimal selection of low mobility, low conductivity buffer ions. Here we demonstrate that changing the sample diameter has a pronounced effect on the sample resistance and this results in dramatic improvements of the signal-to-noise ratio and shorter Ï/2 pulses. We determined these parameters for common 5Â mm NMR tubes under different experimental conditions and compared them to the 2, 3 and 4Â mm tubes, in addition, 5Â mm Shigemi tubes were included since these are widely used. We demonstrate benefits and applicability of studying NMR samples with up to 4Â M salt concentrations in cryogenic probes. Under high salt conditions, best results in terms of short Ï/2 pulses and high signal-to-noise ratios are obtained using 2 or 3Â mm NMR tubes, especially when limited sample is available. The 4Â mm tube is preferred when sample amounts are abundant at intermediate salt conditions.
Related Topics
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Physical and Theoretical Chemistry
Authors
Markus W. Voehler, Galen Collier, John K. Young, Michael P. Stone, Markus W. Germann,