EFFECT OF IONIC-STRENGTH ON THE POLAROGRAPHIC HALF-WAVE POTENTIAL

The shift in the polarographic half-wave potential caused by changes in the concentration of a non-complexing supporting electrolyte was investigated. The depolarizer systems studied were the cadmium(II) and zinc(II) amine complex ions, and the cadmium(II), zinc(II), indium(III) and thallium(I) aquo ions. These systems exhibited half-wave potential shifts that were dependent on five factors affected by the ionic strength of the solution: the activity and diffusion coefficients of the depolarizer ions, the activity of the complexing agent and/or water and the liquid junction potential. An equation was derived relating these factors to the half-wave potential shift and evaluated for the change in the activity coefficient of the depolarizer over the ionic strength range 4-10. As expected, the observed potential shift showed a strong correlation with the charge and primary hydration numbers of the aquo ions.