- Sample Concentration Guidance for Cryoprobe NMR Measurements:
- Biomolecule samples. Prepare at least 0.05mM. higher than 1 mM is prefered as long as solution viscosity does not increase significantly.
- Small molecule samples. About 3mM is sufficient for 13C direct NMR measurements on CP800, and10mM for 13C measurements on CP600. If MW is 200, 10mg/500uL gives 100mM concentration. Please note that for quantification, avoid preparing too high concentration which may cause baseline and lineshape issues.
- NMR tube choices: If you have adequate amount of sample, use a regular NMR tube; If you have limited amount of sample, usage a shigemi NMR tube; If your sample has high salt concentration , use a 3mm NMR tube.
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Sample volume should be a minimum of 250 uL for a Shigemi tube, 160uL for a 3mm/5mm tube, or 500 uL for a regular NMR tube. Insufficient volume may cause bad shimming result, and consequently spectra with poor resolution and line shape. In many cases the sample volume should weight more than the concentration for a good NMR measurement.
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The NMR sample should be homogeneous, free of air bubbles and insoluble substances. High salt concentration and paramagnetic ions should be avoided if possible
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High quality NMR tubes should be used at BioNMR facility, in particular for the 800 MHz spectrometer.
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For volatile organic solvent, or long term use sample, sealing the sample NMR tube with parafilm is highly recommended.
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For aqueous samples,
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D2O concentration should be equal to or higher than 7%, and kept equal to or higher than 7% during titration.
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NaCN 0.02% is recommended for sample buffer to prevent bacterial growth and bio sample degradation.
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Labeling the NMR tube. All samples should be labeled with brief sample information using a labeling tape. Do not write directly on the NMR tube since the ink can easily be erased by mistake. The labeling tape should be wrapped around the NMR tube, not in the shape of a flag.
