SOLUBILITY PARAMETER-BASED METHODS FOR PREDICTING THE SOLUBILITY OF SULFAPYRIDINE IN SOLVENT MIXTURES

Sulfapyridine is used to test the extended Hildebrand approach for pre dicting solubility in dioxane-water mixtures. The method provided good agreement with the experimental data. A modification of this method. that directly relates the logarithm of the mole fraction solubility wi th the solubility parameter of the solvent mixture (delta(1)) gave res ults comparable to that of the extended Hildebrand approach. This sugg ests that the volume fraction of the solvent can be disregarded in the solubility equation. The modified method does not require the knowled ge of the ideal solubility of the drug. A single equation based on the solubilities of several sulfonamides is able to accurately calculate the solubility profile of sulfapyridine from 0 to 70% water in dioxane . Beyond 70% water, the extended Hildebrand method or its simplified f orm provide less errors, but these methods require 12-14 experimental solubilities, whereas the single equation only needs two experimental solubilities.