PREPARING YOUR SAMPLE
Why is it important to know what these impurities dissolve in?
You should try to find a solvent that is compatible with both your sample and any expected impurities. If the impurities are insoluble, they will probably form a separate phase, or float around in the NMR tube as solid particles. Neither situation will lead to high-quality spectra. Check the Handbook of Chemistry and Physics, or the General Solubility Guidelines, to help you find an appropriate solvent. If you cannot identify one that is mutually suitable, you should try to purify your sample further.