Choose a high quality 5 mm NMR tube that is free from defects (e.g. flat bottom, cracked top). The tube should be rated for the instrument you are
using. If you are using the 500 MHz, you should use tubes that are rated for 500 MHz
or better. See Wilmad-Labglass for more information.
Decide on the amount of sample. The sample amount depends on the experiment you are performing. For 1H NMR, 1 mg
to 40 mg is a good range (this assumes small molecules below 700 g/mol). The higher
concentration will lead to difficult shimming and broadened lines. It is recommended
to keep the amount of sample below 20 mg. For 13C NMR and most 2D experiments except
NOESY, the more you use, the better. I have found that 100 mg to 300 mg gives good
signal to noise (S/N) with minimal scans (nt=128). If you use less sample, more scans
may be required.
Choose an appropriate deuterated solvent. If you are not sure of which solvent to use, start with non-deuterated solvents
until you find the appropriate solvent. The most used NMR solvent is deuterated chloroform
(CDCl3), but be careful, it can be acidic and acid sensitive compounds may decompose when
dissolved in CDCl3. Other popular solvents include D2O, acetonitrile-d3, acetone-d6, benzene-d6, DMSO-d6, THF-d8, and CD2Cl2. Many of these solvents are available from the Chemistry Department Stockroom.
Use the appropriate amount of deuterated solvent. Be sure that your sample is completely dissolved, undissolved particulate matter
will lead to poor NMR lineshape. Furthermore, too little solvent will make locking,
shimming difficult. An appropriate volume is 0.7 mL or 5 cm in a 5 mm NMR tube. A
natural inclination when faced with a small amount of sample is to use less solvent
to dissolve the material. This is not advisable because too little solvent can cause
magnetic field gradients due to the difference in magnetic susceptibility between
the solvent and air. This leads to great difficulty in obtaining adequate line shape.
If you must use less solvent, consider using a shigemi tube.
Remember that your solvent may contain dissolved water. Many solvents will contain trace amounts of water when bought and the water content
will increase as you use the solvent. You can store your solvents over molecular sieves
to minimize water, but be sure to filter the solvent prior to using it. For the chemical
shift of water in various solvents, click here.
Cap and label your NMR tube. You are now ready to run an NMR experiment!