The purpose of this study was to develop a novel fluorescence technique employing environment-sensitive fluorescent probes to study phase separation kinetics in hydrated matrices of amorphous solid dispersions (ASDs) following storage at high humidity and during dissolution. The initial miscibility of the ASDs was confirmed using infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Fluorescence spectroscopy, as an independent primary technique, was used together with conventional confirmatory techniques including DSC, X-ray diffraction (XRD), fluorescence microscopy, and IR spectroscopy to study phase separation phenomena. By monitoring the emission characteristics of the environment-sensitive fluorescent probes, it was possible to successfully monitor amorphous-amorphous phase separation (AAPS) as a function of time in probucol-poly(vinylpyrrolidone) (PVP) and ritonavir-PVP ASDs after exposure to water. In contrast, a ritonavir-hydroxypropylmethylcellulose acetate succinate (HPMCAS) ASD, did not show AAPS and was used as a control to demonstrate the capability of the newly developed fluorescence method to differentiate systems that showed no phase separation following exposure to water versus those that did. The results from the fluorescence studies were in good agreement with results obtained using various other complementary techniques. Thus, fluorescence spectroscopy can be utilized as a fast and efficient tool to detect and monitor the kinetics of phase transformations in amorphous solid dispersions during hydration and will help provide mechanistic insight into the stability and dissolution behavior of amorphous solid dispersions.
