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Influence of Air Temperature and Humidity on Dehydration Equilibria and Kinetics of Theophylline.

Touil A, Peczalski R, Timoumi S, Zagrouba F - J Pharm (Cairo) (2012)

Bottom Line: The water content evolutions with time were recorded at several temperatures from 20°C to 80°C and several relative humidities from 4% to 50%.Different mathematical models were used to fit the experimental data.The spatially averaged solution of 2D Fickian transient diffusion equation best represented the water mass loss versus time experimental relationship.

View Article: PubMed Central - PubMed

Affiliation: Ecole Nationale d'Ingénieurs de Gabès (ENIG), Université de Gabès, rue Omar Ibn-Elkhattab, Gabès 6029, Tunisia.

ABSTRACT
The effect of hygrothermal conditions (air temperature and relative humidity) on the dehydration of theophylline monohydrate was investigated. Firstly, the equilibrium states of theophylline were investigated. The data from gravimetric analysis at constant temperature and humidity were reported as desorption isotherms. The PXRD analysis was used to identify the different polymorphic forms of theophylline: the monohydrate, the metastable anhydrate, and the stable anhydrate. Solid-solid phase diagrams for two processing times were proposed. Secondly, the dehydration kinetics were studied. The water content evolutions with time were recorded at several temperatures from 20°C to 80°C and several relative humidities from 4% to 50%. Different mathematical models were used to fit the experimental data. The spatially averaged solution of 2D Fickian transient diffusion equation best represented the water mass loss versus time experimental relationship. The dehydration rate constant was found to increase exponentially with air temperature and to decrease exponentially with air relative humidity.

No MeSH data available.


Related in: MedlinePlus

TGA record for commercial and recrystallized theophylline.
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fig2: TGA record for commercial and recrystallized theophylline.

Mentions: DSC and TGA curves for the recrystallized and commercial theophylline are shown in Figures 1 and 2. The DSC curve of the recrystallized product showed a broad two-split endothermic peak around 60–90°C and a sharp endothermic peak at 272°C. The first endothermic peak was due to dehydration and corresponded to the weight loss of 9.3% in the range from 60 to 80°C on the TGA curve. The stoichiometric weight loss value (calculated for one mol of water) was almost identical to the value obtained from the TG analysis. Thus, the recrystallized product corresponded effectively to theophylline monohydrate. The second endothermic peak was due to the melting of the anhydrous form. The broadness and split of the dehydration peak were possibly due to the broadness and bimodal character of the hydrated form crystal size distribution (available but not presented here). The dehydration was perhaps initiated with smaller crystals and ended with bigger ones as the kinetics constants could be dependent on the particle size.


Influence of Air Temperature and Humidity on Dehydration Equilibria and Kinetics of Theophylline.

Touil A, Peczalski R, Timoumi S, Zagrouba F - J Pharm (Cairo) (2012)

TGA record for commercial and recrystallized theophylline.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4595972&req=5

fig2: TGA record for commercial and recrystallized theophylline.
Mentions: DSC and TGA curves for the recrystallized and commercial theophylline are shown in Figures 1 and 2. The DSC curve of the recrystallized product showed a broad two-split endothermic peak around 60–90°C and a sharp endothermic peak at 272°C. The first endothermic peak was due to dehydration and corresponded to the weight loss of 9.3% in the range from 60 to 80°C on the TGA curve. The stoichiometric weight loss value (calculated for one mol of water) was almost identical to the value obtained from the TG analysis. Thus, the recrystallized product corresponded effectively to theophylline monohydrate. The second endothermic peak was due to the melting of the anhydrous form. The broadness and split of the dehydration peak were possibly due to the broadness and bimodal character of the hydrated form crystal size distribution (available but not presented here). The dehydration was perhaps initiated with smaller crystals and ended with bigger ones as the kinetics constants could be dependent on the particle size.

Bottom Line: The water content evolutions with time were recorded at several temperatures from 20°C to 80°C and several relative humidities from 4% to 50%.Different mathematical models were used to fit the experimental data.The spatially averaged solution of 2D Fickian transient diffusion equation best represented the water mass loss versus time experimental relationship.

View Article: PubMed Central - PubMed

Affiliation: Ecole Nationale d'Ingénieurs de Gabès (ENIG), Université de Gabès, rue Omar Ibn-Elkhattab, Gabès 6029, Tunisia.

ABSTRACT
The effect of hygrothermal conditions (air temperature and relative humidity) on the dehydration of theophylline monohydrate was investigated. Firstly, the equilibrium states of theophylline were investigated. The data from gravimetric analysis at constant temperature and humidity were reported as desorption isotherms. The PXRD analysis was used to identify the different polymorphic forms of theophylline: the monohydrate, the metastable anhydrate, and the stable anhydrate. Solid-solid phase diagrams for two processing times were proposed. Secondly, the dehydration kinetics were studied. The water content evolutions with time were recorded at several temperatures from 20°C to 80°C and several relative humidities from 4% to 50%. Different mathematical models were used to fit the experimental data. The spatially averaged solution of 2D Fickian transient diffusion equation best represented the water mass loss versus time experimental relationship. The dehydration rate constant was found to increase exponentially with air temperature and to decrease exponentially with air relative humidity.

No MeSH data available.


Related in: MedlinePlus