Analytical Techniques and Strategies for Salt/Co-crystal Characterization
Salts and co-crystals provide numerous options for tailoring the physical properties of an active pharmaceutical ingredient to meet the needs of a drug product. Navigating the frequently complex solid form landscapes of drugs, their salts and co-crystals, however, requires ready access to reliable solid-state characterization techniques to ensure that a suitable form is identified and a robust crystallization process is developed to select for it. Crystallography, spectroscopy, microscopy, thermal techniques and moisture sorption analysis are routinely used to examine the structures and properties of pharmaceutical solids. In this contribution, analytical techniques and strategies for characterizing salt and co-crystal forms, probing ionization in the solid state and assessing thermodynamic stability are presented.