Biomedical subjects
Publications and source records attributed to Keith B Oldham.
An accurate formula exists for describing the decay of the current following the imposition of extreme concentration polarization on a disk electrode under diffusion-controlled conditions. It has been amply validated by diverse simulations and is presented here in a more compact form than hitherto. The formula finds application beyond the realm of potential-step chronoamperometry.
Fourier transform analysis of ramped square-wave voltammograms indicates the availability of a novel form of kinetic selectivity for surface-confined electron-transfer processes. Thus, for all the even harmonic components, quasi-reversible processes are sensitive to the surface coverage, the reversible potential, the electron-transfer rate constant (k(0')), and the electron-transfer coefficient (alpha), as well as to the amplitude (DeltaE) and frequency (f) of the square wave and dc scan rate. Additionally, it is insensitive to background capacitance current. In contrast, reversible processes and background currents are predicted to be absent from the even harmonics and only detectable in the odd harmonic components. The square-wave voltammetry of the surface-confined quasi-reversible azurin process azurin[Cu(II)] + e(-) right arrow over left arrow azurin[Cu(I)] at a paraffin-impregnated graphite electrode has been employed as a model system to test theoretical predictions. Most voltammetric characteristics of the even harmonic components obtained from the Fourier analysis are consistent with electrode kinetic values of k(0') = 90 s(-1) and alpha = 0.48, although some nonideality possibly due to kinetic dispersion also is apparent. Conditions also have been determined under which a readily generated waveform constructed from the Fourier series of sine waves produces voltammograms that are essentially indistinguishable from those predicted when an ideal square wave is employed.
It has been found empirically that, for an E(rev)C(irrev) process, the forward/backward ratio of the peak height magnitudes in cyclic voltammetry equals 1 + ktau, where k is the rate constant of the chemical reaction and tau is the time required for the scan to travel between the half-wave and reversal potentials. The relationship is largely independent of the scan rate and the reversal potential, except insofar as these influence tau. Though not exact, the relationship is obeyed closely enough to provide accurate rate constants under favorable conditions. The utility of this simple formula in extracting homogeneous kinetic information is demonstrated using experimental data for the electron-transfer-induced isomerization of an octahedral manganese complex. An explanation of the relationship is presented, as is a more exact formula that reduces to 1 + ktau when k is small. A semiquantitative explanation of the relationship is provided.