Abstract
Aspirin crystals having different types of habits were prepared by recrystallization of commercial products from various solvents. The difference in crystal habits was investigated crystallographically and optically by the use of a polarizing microscope to measure habit parameters a, b, and c. The dissolution behavior of these crystals was studied in an artificial gastric juice, and the dissolution constants were calculated by means of the Noyes-Whitney equation using the specific surface areas obtained from the habit parameters. It was found that the dissolution constants of crystals with different habits were not constant, and it seems that the values depend upon the ratio of the area of (001) to the sum of the areas of the remaining faces. It was also found that aspirin dissolved more easily when it was powdered than would be expected from the increased surface area. This phenomenon might be a result of the distortion of crystals which was observed under the polarizing microscope.
