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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

Predicted dehydration curves of theophylline monohydrate according to different models.
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fig14: Predicted dehydration curves of theophylline monohydrate according to different models.

Mentions: The best fit over all experimental conditions was obtained with the model C. The k parameter was considered as a function of air temperature and relative humidity and was represented by the classical Arrhenius equation:(1)lnk=lnk0−EaRT.According to the above equation, ln  k was plotted as function of the inverse of the temperature. As the relative humidity imposed by salt solutions (see Table 1) varies slightly with temperature, the relative humidity values given in Figure 12 and Table 4 were averaged over the considered temperature domain (20–80°C). From the linear fits (see Figure 12), the activation energy Ea (values given in Table 4) and the preexponential coefficient k0 (values given in Figure 13) were calculated as function of relative humidity. These values were close to those calculated by Suzuki et al. [2] and Agbada and York [14]. The activation energy appeared to be varying very little with relative humidity and was approximated by its average value (see Tables 4 and 5). On the contrary, the logarithm of the preexponential factor k0 was found to decrease linearly with the relative humidity (see Figure 14).


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)

Predicted dehydration curves of theophylline monohydrate according to different models.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig14: Predicted dehydration curves of theophylline monohydrate according to different models.
Mentions: The best fit over all experimental conditions was obtained with the model C. The k parameter was considered as a function of air temperature and relative humidity and was represented by the classical Arrhenius equation:(1)lnk=lnk0−EaRT.According to the above equation, ln  k was plotted as function of the inverse of the temperature. As the relative humidity imposed by salt solutions (see Table 1) varies slightly with temperature, the relative humidity values given in Figure 12 and Table 4 were averaged over the considered temperature domain (20–80°C). From the linear fits (see Figure 12), the activation energy Ea (values given in Table 4) and the preexponential coefficient k0 (values given in Figure 13) were calculated as function of relative humidity. These values were close to those calculated by Suzuki et al. [2] and Agbada and York [14]. The activation energy appeared to be varying very little with relative humidity and was approximated by its average value (see Tables 4 and 5). On the contrary, the logarithm of the preexponential factor k0 was found to decrease linearly with the relative humidity (see Figure 14).

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