Drug hydrate systems and dehydration processes studied by terahertz pulsed spectroscopy

Terahertz pulsed spectroscopy was used to distinguish between different hydrate systems. In the example of four pharmaceutical materials lactose, carbamazepine, piroxicam and theophylline it was demonstrated that all different hydrate and anhydrate forms exhibit distinct spectra in the far infrared. Furthermore the dehydration of theophylline monohydrate was characterised in situ. Here, a phase transition from the monohydrate to the anhydrous form was observed, followed by evaporation of the hydrate water in a second step. The rotational spectrum of water vapour is very characteristic in the far infrared and can easily be discerned from the terahertz spectrum of the solid state form.