When a  solid is investigated using the NMR technique, signals tend to be broad and the fine structure, which is of most interest to scientists, cannot be resolved. Consequently, solid samples are usually dissolved in a suitable solvent prior to acquisition. The same goes for  liquid samples. In organic solvents, small amount of a reference compound may be added. However, to achieve best results the sample should be as pure as possible. Signals from  impurities will at best make the spectrum unnecessarily complicated and at worst mask genuine signals. Particular care should be taken to ensure that the sample is free of  magnetic impurities as these can distort the magnetic field and hence degrade the spectrum resolution. Solid impurities can be most easily removed by filtering. For samples in  organic solvents, dissolved water can be removed as far as possible by thoroughly drying the sample prior to dissolution.