NMR to Distinguish Solid Polymorphs

Some solids have a number of different polymorphs (or phases). Being able to distinguish different polymorphs is very important for the pharmaceutical industry. Solid State NMR is able to distinguish between them. In the figure below is the 13C CPMAS spectrum of the solid amino acid, methionine acquired on a Bruker AVANCE 500 NMR spectrometer. The spectrum clearly shows two signals for each type of carbon.

When the temperature is varied the intensity ratio of the peaks changes as one polymorph becomes more favored than the other.