Method of Isopotential Solutions

It has been mentioned in Chapter 2 that a series of solutions of complex compounds with constant M concentration, which according to Eq. (2.3) unambiguously determines the electrode potential, can always be prepared. Bulk concentrations of free ligand and complex particles are different in such isopotential solutions (IPSs). The composition of the IPS series can be calculated using material balance equations and setting the same [M ] but different [L] values. Further, we shall see that the exchange current density measurements in the IPS series enable the EAC composition to be determined in a rather simple manner with no limitations mentioned in Section 6.1. 

Let us briefly discuss the theory of the IPS method [10]. In formal electrochemistry, the exchange currency density is the cathodic or anodic component of current density i in the equilibrium state, where E = and i = 0. The following expression can be obtained from the kinetic equation written for the charge transfer process (Eq. (2.5))  

If several charge transfer reactions involving different complex species ML (j = p,p + 1, occur, the exchange current density ig consists of 

If the stepwise charge transfer process proceeds in accordance with the reactions (5.9) and (5.10), the exchange current densities of both steps are to be determined. In this case, the following are vaUd for the equilibrium state 

Similar analysis shows that the following equations are valid for two consecutive one-electron transfers  

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