A sample melt technique has been developed for the rapid identification by infrared spectra of polymorphs and solvates. Excellent spectra are obtained; no decomposition or rearrangements have been detected in studies with 35 compounds, which included 25 steroids. Resolidified melt spectra of known polymorphs have been identical. The problems of low solubility and unusable regions of the spectra encountered in solution studies are avoided. In the case of solvates, the solvent may be identified by its spectrum in the gaseous or liquid state, and the spectrum of the solvent-free compound may be determined on the resolidified melt.
Marvin F. Grostic and George E. Bronson, "Use of Resolidified Melts in Infrared Spectroscopy: Application to Polymorphism and Solvation Studies," Appl. Spectrosc. 15, 157-159 (1961)