Assessing dissolution kinetics of powders by a Single Particle approach

The dissolution kinetics of powders is of critical importance in many industrial and consumer applications, ranging from food and pharmaceutical products, to chemicals, fertilizers, paints, etc. In the food industry in particular, it is one of the relevant factors that defines product quality. The common approach for studying the dissolution kinetics of powders could be characterized as a "bulk approach" indicating that the dissolution process is studied by utilizing a considerable amount of powder. In the present work, we suggest a new methodology based on a "single particle" approach. A single particle is the basic unit composing the bulk of a powder, and vast information could be gained by understanding its dissolution kinetics. The dissolution of single particles was measured by means of a microscopy-based experimental method with appropriate image analysis algorithms. The effects of various liquids and their physical properties on the dissolution kinetics were quantified. A mathematical model based on a shrinking sphere was utilized to describe the dissolution process. A rate constant was derived from the experimental data for each tested condition and correlated to the viscosity of the dissolving medium. A significant effect, mostly at low viscosity values was found. The obtained results are in accordance with the diffusive behavior as predicted from the Einstein-Stokes equation. Calorimetric measurements were carried out and correlated with the rate constant derived from measurements at the single particle level. It is proposed that the dissolution process might not be only mass transfer limited, but also heat transfer mechanism might have a significant effect on the overall rate.