The flowability and dispersion behaviour are two important physicochemical properties of pharmaceutical formulations for dry powder inhalers. They are usually affected by environmental conditions, such as temperature and relative humidity. However, very few studies have been focused on the relationship between the two properties and their dependence on relative humidity during storage.
The refractive index is used to measure solids, liquids, and gases. Most commonly it is used to measure the concentration of a solute in an aqueous solution, and like density, it is used to characterise how a material behaves.
The dissolution rate is a measure of the actual release rate of the compound at the given particle size etc. in an aqueous media.