Use of the 1,1′-dimethylferrocene oxidation process for the calibration of the reference electrode potential in organic solvents immiscible with water

Cyclic voltammetric oxidation of 1,1′-dimethylferrocene (DMFc) at an Au disc electrode in dichloromethane, 1,4-dichlorobutane, 1,6-dichlorohexane, chlorobenzene, 1,2-dichlorobenzene, 1,2-dichloroethane, 2-nitrophenyl octyl ether and nitrobenzene is used to estimate the standard potential E0(SHE) of the DMFc+/DMFc redox system vs. the standard hydrogen electrode in these solvents. Results indicate that E0(SHE) tends to decrease a little with the increasing solvent permittivity probably due to a stabilization of the oxidized ferrocene form by its interaction with polar solvent molecules. Estimated values of E0(SHE) and Au electrode voltammetry of DMFc are then used to calibrate the potential of the bis(triphenylphosphoranylidene)ammonium+ (BTPPA+) ion-selective type reference electrode (RE), which has been often employed in polarization studies at the interface between two immiscible electrolyte solutions. It is shown that when BTPPA+ is present in the form its chloride salt, the reference potential comprises the mixed potential difference due to the balance of currents corresponding to the co-extraction of the BTPPA+ and Cl− ions into the organic solvent phase of RE. Calibration is verified by measuring the values of E0(SHE) for the parent ferrocene and two other ferrocene derivatives, n-butylferrocene and decamethylferrocene, which are found to agree well with literature data.