Isotope-Edited Infrared Spectroscopy for Efficient Discrimination between Pharmaceutical Salts and Cocrystals

Isotope-edited infrared spectroscopy using carboxylic acids selectively labeled with ¹³C is proposed herein for the efficient discrimination of pharmaceutical salts and cocrystals, whereby proton-transfer probe vibrations are highlighted by isotope shifts. This new technique can accurately discriminate even a confusing salt from a cocrystal for the traditional method, highlighting the diagnostic peaks. In addition, the established technique also provided the OH in-plane bending vibrations corresponding to intermolecular hydrogen bonding at the carbonyl oxygens of the cocrystals. The technique will accelerate the discrimination, which is a critical process in cocrystal development.