Influence of supporting electrolyte activity on formal potentials measuredfor dissolved internal standards in acetonitrile

Osmotic coefficients are determined for tetra-n-butylammonium perchorate (T BAClO(4)) in acetonitrile. Filter equations are fit to the data, and the re sulting fitting parameters are used to calculate activity coefficients for TBAClO(4). The activity coefficients are used to control electrolyte activi ties so that the junction potential across a permselective anion exchanger is near zero. An electrochemical cell containing this junction is used to e xamine the influence of electrolyte activity on the formal potentials measu red for ferrocene/ferrocenium and decamethylferrocene/decamethylferrocenium . It is clear that the oxidized forms of both redox couples are ion-paired with perchlorate anions in the supporting electrolyte and that this ion-pai ring has a significant influence on the formal potentials. (C) 2001 Elsevie r Science B.V. All rights reserved.