CHRONOAMPEROMETRY OF UNCHARGED SPECIES UNDER THE CONDITIONS OF DEFICIENCY OF SUPPORTING ELECTROLYTE - EXPERIMENT VERSUS THEORY

Chonoamperometry of ferricene in acetonitrile containing a small amoun t of supporting electrolyte was studied to verify the theoretical mode l developed by Hyk et al. (W. Hyk, M. Palys and Z. Stojek, J. Electroa nal. Chem., 415 (1996) 13). Some minor extensions were made in this mo del to adjust it better to the case studied. The experimental chronoam perograms were found to agree well with the theoretical predictions. T he biggest deviations were observed for small support ratios. These de viations can be explained by the uncontrolled presence of ionic impuri ties in the solvent. The impurities influence significantly the conduc tivity of the solution for support ratios (ratio of concentration of s upporting electrolyte and ferrocene) smaller than 0.00075, and cannot be included explicitly in the theoretical model. The influence of the geometry of the electrode and the effect of the double layer capacitan ce are discussed. A possibility of evaluating the total ion level and the formal potential of the system investigated, by fitting an experim ental curve to the theoretical one, is also presented.