The three-dimensional arrangement of drug molecules in the solid state is of critical importance to physical properties such as solubility and bioavailability. Drugs often exhibit multiple stable polymorphs (crystalline packing motifs) that are interconvertible through mechanisms such as temperature changes, choice of crystallization solvent, and even ambient humidity. These various pharmaceutical polymorphs each exhibit unique identifying crystal lattice vibrations that occur in the THz region of the electromagnetic spectrum. Terahertz spectroscopy provides a rapid non-destructive method for the real-time monitoring of pharmaceutical polymorph content in bulk APIs (active pharmaceutical ingredients) for manufacturing line quality assurance and also in final formulated products to ensure long-term stability.
King, Matthew D.; Buchanan, William D.; Korter, Timothy M.. Identification and Quantification of Polymorphism in the Pharmaceutical Compound Diclofenac Acid by Terahertz Spectroscopy and Solid-State Density Functional Theory. Analytical Chemistry (Washington, DC, United States) (2011), 83(10), 3786-3792.
King, Matthew D.; Buchanan, William D.; Korter, Timothy M.. Understanding the terahertz spectra of crystalline pharmaceuticals: Terahertz spectroscopy and solid-state density functional theory study of (S)-(+)-ibuprofen and (RS)-ibuprofen. Journal of Pharmaceutical Sciences (2011), 100(3), 1116-1129.