Determination of glass transition temperature and in situ study of the plasticizing effect of water by inverse gas chromatography.
OBJECTIVE
To use an inverse gas chromatographic (IGC) method to determine the glass transition temperature (Tg) of some amorphous pharmaceuticals and to extend this technique for the in situ study of the plasticizing effect of water on these materials.


METHODS
Amorphous sucrose and colyophilized sucrose-PVP mixtures were the model compounds. Both IGC and differential scanning calorimetry (DSC) were used to determine their Tg. By controlling the water vapor pressure in the IGC sample column, it was possible to determine the Tg of plasticized amorphous phases. Under identical temperatures and vapor pressures, the water uptake was independently quantified in an automated water sorption apparatus.


RESULTS
The Tg of the dry phases, determined by IGC and by DSC, were in very good agreement. With an increase in the environmental relative humidity (RH), there was a progressive decrease in Tg as a result of the plasticizing effect of water. Because the water uptake was independently quantified, it was possible to use the Gordon-Taylor equation to predict the Tg values of the plasticized materials. The predicted values were in very good agreement with those determined experimentally using IGC. A unique advantage of this technique is that it provides complete control over the sample environment and is thus ideally suited for the characterization of highly reactive amorphous phases.


CONCLUSIONS
An IGC method was used (a) to determine the glass transition temperature of amorphous pharmaceuticals and (b) to quantify the plasticizing effect of water on multicomponent systems.
Surana
Rahul
R
Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Randall
Linda
L
Pyne
Abira
A
Vemuri
N Murti
NM
Suryanarayanan
Raj
R
D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002849:Chromatography, Gas / Q000379:methods; D018360:Crystallography, X-Ray; D044367:Phase Transition; D010968:Plasticizers / Q000737:chemistry*; D011205:Povidone / Q000737:chemistry; D013395:Sucrose / Q000737:chemistry; D013678:Technology, Pharmaceutical; D044366:Transition Temperature; D014867:Water / Q000737:chemistry*
D010968:Plasticizers; D014867:Water; D013395:Sucrose; D011205:Povidone