*2.3.7 Freeze-drying*

Freeze drying, in principle recognized as lyophilization, has primarily been employed as dispensing scheme for a range of products, including foodstuff and drugs. The procedure functions to sublimate the component directly from the solid phase to the gas phase by decreasing the ambient pressure to cause the freezing of

H2O within the component also known as sublimation. It has also recently emerged as a viable process for preparing novel solid-state forms of co-crystals. Eddleston et al. reported the preparation of new theophylline:oxalic acid co-crystals by lyophilization. Co-crystallization occurs through an amorphous state that is produced as solvent sublimes throughout lyophilization [38].
