The use of dynamic vapour sorption and near infra-red spectroscopy (DVS-NIR) to study the crystal transitions of theophylline and the report of a new solid-state transition.
This study was undertaken to see if the combined technique of DVS-NIR could add to the understanding of transitions between physical forms of theophylline. There was excellent correlation between the mass changes and the intensity of the NIR peaks, showing that the hydrate was being formed and lost. This was characterised by the peaks at 1478 and 1972 nm representing an -OH deformation. NIR spectra for desorption shows that the dehydrate retains partial structure of both the anhydrate and hydrate crystal lattices. During rehydration of the dehydrate a new transition was discovered. An unexpected mass loss occurred between 40 and 50% RH. Usually, a mass loss during water sorption is characteristic of crystallisation of an amorphous material, although in this case it could be that the sample is crystalline. NIR data showed that during this transition the dehydrate peaks reverted back to the peak positions seen for anhydrous theophylline. The absorption of water into the dehydrate allowed the freedom of movement for the stable anhydrous lattice to form. It was concluded that DVS-NIR is a useful tool to study solid-state transitions and that the transition exists for conversion of theophylline dehydrate to anhydrate which is facilitated through water sorption.
Vora
Ketan L
KL
Department of Pharmaceutics, School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK.
Buckton
Graham
G
Clapham
David
D
D003460:Crystallization; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013806:Theophylline / Q000032:analysis* / Q000737:chemistry; D014835:Volatilization
D013806:Theophylline