From the hydrogen spectrum, if there are many small peaks with less than one integral, it is possible that the sample is an impurity in the sample. The quantification of the carbon spectrum can also be used to identify the purity using a gated decoupling technique.
Each method has its own limitations, such as the purity identification based on the hydrogen spectrum. If there are many small peaks with less than one integral, it is possible to make the active protons in the sample be identified based on the purity of the soft ionization mass spectrum. The molecular weight of the molecule cannot be detected as it is the target.
For compound purity, there is no 100% pure compound in the world. It is hoped that how high the purity should be related to the purpose. For example, if you want to determine the structure by nuclear magnetic resonance, it is generally required to have a purity of 95%. If you want to measure EI-MS, the higher the purity, the better. More than 99%.
None of the above methods can distinguish the corresponding isomers.