Analysis of Voltammetric Half-Wave Potentials in Low Ionic Strength Solutions and Voltammetric Measurement of Ion Impurity Concentrations
Technical rept. no. 11, 1 Jan-31 Oct 1990,
MINNESOTA UNIV MINNEAPOLIS DEPT OF CHEMICAL ENGINEERING AND MATERIALS SCIENCE
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An analytic equation is presented that allows the prediction of steady-state voltammetric half-wave potentials as a function of electrolyte concentration in low ionic strength solutions for an electrode of arbitrary geometry and size. The equation is tested for the oxidation of ferrocene in acetonitrile at 2.4 - 20 micro m platinum microdisk electrodes for electrolyte tetra-n-butylammonium perchlorate concentrations between 10-1 and 4 x 10 to the 9th power M, and in acetonitrile solutions containing no intentionally added electrolyte. An analytical method for measuring ion impurity concentration, based on steady-state microelectrode voltammetry, is proposed and used to measure micro M ionic impurities in acetonitrile. The role of ionic solution 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 is proposed.