Ion-selective electrodes for the determination of ionisation constants of sparingly soluble organic bases in aqueous solutions: applications to chlorpromazine and amitriptyline

Abstract

The response of ion-selective electrodes that are sensitive to the protonated species of sparingly soluble organic bases is examined theoretically at various pH values. It is shown that for such bases the potential versus pH plots are unsuitable for the accurate determination of the pK_a. A new method is proposed that can be used to measure the aqueous ionisation constants of organic compounds with low solubilities in water. The method was applied to the organic basic drugs chlorpromazine and amitriptyline. The results obtained were in close agreement with previously reported values.