Analysis of Voltammetric Half-Wave Potentials in Low Ionic Strength Solutions and Voltammetric Measurement of Ion Impurity Concentrations

An analytic equation Is presented that allows the prediction of steady-state voltammetric half-wave potentials as a function of electrolyte concentration in low lonic strength solutions for electrodes of arbitrary geometry and size. The equation is tested for the oxidation of terrocene and reduction of TCNQ in acetonitrile 2.4- and 12.4-µm-radius platinum-microdisk electrodes for electrolyte (tetra-n-butylammonium Perchlorate) concentrations between 10−1 and 4×10−9 M, and in acetonitrile solutions containing no intentionally added electrolyte. An analytical method for measuring the total ionic impurity concentration, based on steady-state microelectrode voltammetry, is proposed and used to measure these impurities in acetonitrile. The role of these impurities on voltammetric measurements in the absence of intentionally added electrolyte is quantified and a criterion for the minimum number of ions required to observe sigmoidally shaped voltammetric curves at microelectrodes Is proposed. © 1991, American Chemical Society. All rights reserved