turbidity. As the solubility limit is progressively exceeded, the turbidity rises. The solubility can be determined by extrapolation as shown in Fig. 5.4. Table 5.10 shows results obtained by this method for some pheno-thiazines and tricyclic antidepressant compounds. Determination of the solubility of weak electrolytes at several pH values provides one method of obtaining the dissociation constant of the drug substance. For basic drugs, equation (5.16) is rearranged to give pH = pKa + log)

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