Arnold Equation Research Articles

Studies on powdered preparation. XVII. Dissolution rate of sulfonamides by rotating disk method.

The disk of sulfonamide was made by compression of the powder and the dissolution rate was measured by rotating it in water under various conditions. The results obtained are : 1. The concentration-time curve of dissolution was obtained with a good reproducibility and it did not depend on the thickness of disk, the size and shape of the flask which contained the liquid, and the depth of the disk from water level. 2. The dissolution rate constant, KT, did not depend on the surface area of the disk and the volume of the liquid of 50 to 200 ml. During the dissolution experiment, disintegration of disk could not be considered to occur. 3. KT did not depend on the compressional pressure to make disk under 1 to 5 tons/cm2. This showed that the dissolution depended on the apparent geometrical surface area, not on the intrinsic surface area of solid. 4. KT was proportional to the square root of rotating velocity of the disk. 5. The activation energy of dissolution of sulfadiazine was about 3.5 Kcal./mole. 6. The values of KT of five kinds of sulfaonamides were quite coincident with the values calculated according to the Arnold equation. The values of saturated concentration, CO, were coincident with the values of solubility, CS, observed. 7. From the results obtained, it would be possible to give the following conclusions : I) From the measurement of dissolution rate by the rotating disk method, KT and CO can be obtained separately with a high confidence on the value. ii) The dissolution of sulfonamide is in accordance with the Noyes-Nernst equation concerning the transport controlled dissolution. The Levich Equation is also established.