The only way to obtain useful data is to have well prepared samples in high quality nmr tubes. Do not buy nmr tubes in bulk packets that do not have labels specifying what they are. You will not know the quality of these tubes. At the minimum you will get poor results and the worst they will damage the nmr instruments There are many grades of nmr tubes. Below is a list of nmr tubes that we have found to work well on our instruments. Quality nmr tubes from other vendors might work as well; we are happy to help testing these tubes
For instruments of 500 MHz and less.
Norell (nmrtubes.com) 507-HP-7 (these are sold in the VWR stockroom)
Wilmad (willmad-labglass.com) 527-PP-7
New Era (https://newera-spectro.com) NE-HP5
For instruments of 700 MHz and 800 MHz you can use the tubes above but you will get better results from tubes that are specified for those field strengths.
Samples of the required material should be dissolved in an appropriate DEUTERATED solvent. The deuterated solvent serves two purposes. First it acts as the lock material and secondly, if you are running a proton spectrum, it removes the presence of a large solvent peak.
Use an appropriate concentration.
For a proton spectrum on the majority of organic materials of molecular weight of under 500 one needs between 3 mg to 5 mg dissolved in 0.7 ml of a deuterated solvent. Since 13C is of lower natural abundance and lower sensitivity one needs more material to be able to obtain data in a reasonable amount of time. In this case one should use a minimum of 25 mg dissolved in 0.7 ml of deuterated solvent.
Solutions samples should be just that, solutions. There should be no particulate matter in the NMR tube. If necessary filter your samples. Gel like samples will be difficult to shim and give very broad lines.
Instructions for the Bruker Instruments:
Instructions for the Varian Instruments: