Polymorph Screening Using Near-Infrared Spectroscopy

Near-infrared spectroscopy was utilized as a polymorph screening method. A model compound (sulfathiazole) was recrystallized from various solvents, and the crystals were milled using a planetary ball mill and compressed using a hydraulic press. The polymorphism of recrystallized and processed samples and the effect of processing on the polymorphism of sulfathiazole was studied by near-infrared (NIR) spectroscopy and verified by X-ray powder diffraction (XRPD) and thermal analysis. Polymorphism and the degree of crystallinity of the processed samples were studied, and NIR spectroscopy proved to be a fast tool for polymorph screening and monitoring the processing-induced transformations. After clustering of the NIR spectra of various samples, XRPD and complementary methods can be applied to a more thorough analysis of different clusters. This approach provides a timesaving improvement for the polymorph analysis in the case of large number of samples.