IMPROVEMENT AND ESTIMATION OF PRECISION IN CYCLIC VOLTAMMETRY - THERMODYNAMIC AND KINETIC DETERMINATIONS IN CHEMICALLY REVERSIBLE-SYSTEMS

Systematic determination of cyclic voltammetric peak potentials for the reduction of anthracene in N,N'-dimethylformamide (DMF), taken as a model example of a (chemically) reversible reaction, from non-filtered digitized data, using a cadmium amalgam electrode in DMF, indicates a precision of 0.3-0.4 mV at the level of each individual voltammogram. Filtering of the raw data may give the impression of an improvement in the precision in the sense that it decreases the random error. However, it also correlatively introduces a rapidly growing systematic error which makes the cure worse than the illness. Reproducibility tests carried out under typical conditions of a peak potential vs. scan rate investigation (i.e. over hours) show that the error is of the order of 1 mV for each scan rate. Reliable determinations of the standard rate constant may be obtained from peak potential separations in the 10-200 V s-1 range of scan rate even though the reaction is particularly fast (the standard rate constant uncorrected for double-layer effects is 1.6+/-0.3 cm s-1). The error (about 20%) is, however, a reflection of the upper limitation of the scan rates.