Direct Measurement of Amorphous Solubility

Abstract

Amorphous materials exhibit distinct physicochemical properties compared to their respective crystalline counterparts. One of these properties, the increased solubility of amorphous materials, is exploited in the pharmaceutical industry as a way of increasing bioavailability of poorly water-soluble drugs. Despite the increasing interest in drug amorphization, the analytical physicochemical toolbox is lacking a reliable method for direct amorphous solubility assessment. Here, we show, for the first time, a direct approach to measure the amorphous solubility of diverse drugs by combining optics with fluidics, the single particle analysis (SPA) method. Moreover, a comparison was made to a theoretical estimation based on thermal analysis and to a standardized supersaturation and precipitation method. We have found a good level of agreement between the three methods. Importantly, the SPA method allowed for the first experimental measurement of the amorphous solubility for griseofulvin, a fast crystallizing drug, without the use of a crystallization inhibitor. In conclusion, the SPA approach enables rapid and straightforward determination of the supersaturation potential for amorphous materials of less than 0.1 mg, which could prove highly beneficial in the fields of materials science, analytical chemistry, physical chemistry, food science, pharmaceutical science, and others.