The NMR Sample
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7.3 Sample Handling
It is good practice to filter NMR solutions directly into the sample tube to keep the solution
free from dust and other contamination.
Note: The sample tube should always be held by the top!
A typical procedure to prepare a sample might be as follows:
1. For a solid sample using a 5 mm tube dissolve up to 20 mg of the sample in about 0.6 cm
3
of the selected solvent (for 10 mm tubes dissolve 80 mg in 2.5 cm
3
). Typically for a liquid
sample, and when observing protons, dissolve 20% sample in 80% deuterated solvent.
2. Add a small amount (~0.1%) of reference compound Tetramethylsilane (TMS). Make sure
the TMS signal is smaller than the most intense sample or solvent signal (otherwise the
signal-to-noise ratio is wasted because of low receiver gain).
3. Filter the solution into the sample tube through a Pasteur pipette containing a small plug
of Kimwipe.
4. Filter 0.2 cm
3
of solvent through the filter into the tube. The resulting solution should have
a depth of three to four centimeters.
5. Close the tube with a cap, seal the top with parafilm to reduce evaporation and label the
tube near the top. Be careful to ensure that the cap, parafilm and label are concentric or
otherwise they will adversely affect sample spinning.
Note: Some problems may occur when using glass fiber for filtering the sample, especially
when you want to measure T
1
.
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