IONICALLY MODIFIED ELECTRODES FOR USE IN NONPOLAR FLUIDS

The addition of water to the supercritical fluid of carbon dioxide or nitrous oxide allows for voltammetry to be performed on analytes dissolved in these solvents. Experimental data show that an amount of water in excess of its solubility must be added to the electrochemical cell in order to minimize ohmic distortion. This, along with the observed shapes of voltammograms taken in these systems, indicates that water film formation is taking place on the surface of the electrodes. Electrodes coated with tetrahexylammonium nitrate ((THA)-NO3) are shown to be useful in detecting species dissolved in supercritical CO2 and N2O. (THA)NO3 (mp 69-degrees-C) is molten at ambient temperatures under the supercritical fluids due to dissolution of the fluids in the molten salt. Analytes dissolved in supercritical CO2 or N2O and liquid heptane partition into molten (THA)NO3 films on electrodes to give voltammograms free from ohmic distortion. The voltammetric waves of ferrocene, anthracene, and 9, 10-diphenylanthracene are shown to be chemically irreversible in the molten salt. The chemical irreversibility of these analytes is not evident when (THA)NO3 is used as a conventional electrolyte in acetonitrile solutions. Post-SFC column detection of FeCp2 at a molten (THA)NO3 film electrode yields a detection limit of 0.1 ng.