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.
Typical procedures 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 cm3 of the chosen solvent (for 10 mm tubes dissolve 80 mg in 2.5 cm3). 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 cm3 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.