Ion-pair formation of Bi(III)-iodide with some nitrogenous drugs and its application to pharmaceutical preparations.

A systematic spectrophotometric study on the ion-pair formation of Bi(III)-iodide with amineptine hydrochloride, piribedil and trimebutine maleate is carried out. The optimal experimental conditions pH, concentration of Bi(III) nitrate, potassium iodide; and the nature and amount of organic solvent have been studied. The ion pairs are soluble in 1,2-dichloroethane and the optimum pH range is 2.0-2.8. By application of the methods of Sommer and Job involving non-equimolar solutions, the conditional stability constant (log K') of the Bi(III) piridedil ion pair (1:1) at the optimum pH of 2.4 and an ionic strength (mu) 0.1 M, was found to be 5.436. The validity of Beer's law has been tested in the concentration range 5-50 microg ml(-1) in the organic layer, the relative standard deviation is less than 1%. The method is applied to the determination of these drugs in tablets without interference.