Nonlinear regression analysis of steady‐state voltammograms obtained at microelectrodes

Abstract

Abstract Nonlinear regression was applied to the analysis of steady‐state voltammograms obtained at carbon fiber microelectrodes. Reversible regression models were used to analyze data for oxidation of ferrocene in acetonitrile with and without added electrolyte. This analysis constitutes a test for reversibility of the redox couple. An estimate of cell resistance in highly resistive media was obtained by including ohmic drop in the model for reversible electron transfer. This allows computation of „resistance‐free”︁ voltammograms obtained in that medium. A general model for steady‐state voltammograms of quasi‐reversible electrode reactions was used to estimate simultaneously apparent standard heterogeneous electron transfer rate constants ( k 0′ ), formal potentials, and electrochemical transfer coefficients for ferrocyanide and the Co(II)/Co(I) couple of vitamin B 12r . Precision for ferrocyanide with a k 0′ of 0.023 cm/sec was about ±30%. Results on ferrocene suggest an upper limit for estimating k 0′ of about 1–2 cm/sec when the signal/noise ratio (S/N) is large. Data for the quasi‐reversible Co(II)/Co(I) couple of vitamin B 12r showed that results of reasonable precision and accuracy can be obtained for systems with poor S/N.