SOLUBILITY CHARACTERIZATION OF PRACTICALLY INSOLUBLE DRUGS USING THE COULTER-COUNTER PRINCIPLE

A new method was evaluated to determine the solubility of some sparingly soluble materials, using a Coulter counter TA II. This method was based on characterizing the remaining undissolved amount of the suspended material for different initial amounts added, after a specific agitation time. The amounts remaining were then plotted vs the initial concentration of each respective suspension. After applying linear regression and an extrapolation procedure the aqueous solubility was obtained from the intercept. The most important advantage of this method is, firstly, the possibility to determine the solubility of a compound down to 0.1 ppm (mu g/ml) or less and, secondly, its applicability to preformulation studies, which require a quick and accurate estimation of solubility using a minute amount of sample. It could be of especial importance when no conventional assay procedure, such as a photometric method, exists.