Dielectric spectroscopy for the determination of the glass transition temperature of pharmaceutical solid dispersions

Abstract

The purpose of this study was to evaluate analytical techniques for the measurement of the glass transition temperature of HPMC and formulated solid dispersions thereof. Unmodified samples of various grades of HPMC and solid dispersions of HPMC and itraconazole produced by hot melt extrusion were analyzed by thermomechanical analysis, differential scanning calorimetry, thermally stimulated depolarization current and dielectric spectroscopy. It was found that dielectric spectroscopy offers the best accuracy and reproducibility for analysis of the base HPMC powders regardless of the substitution type or viscosity grade and that the obtained results were not frequency dependent. The results of dielectric measurements of solid dispersions prepared by hot melt extrusion were compared with predicted values of the Gordon–Taylor equation. It was found that time–temperature superposition effects and small molecule frequency dependence makes broadly applying determination of the glass transition temperature in drug dispersions by dielectric spectroscopy prohibitively difficult.

• Hot melt extrusion
• HPMC
• hypromellose
• hydroxypropylmethylcellulose
• itraconazole
• thermomechanical analysis
• thermally stimulated depolarization current

Declaration of interest

The authors have no declarations of interest.