Anal. Chem. 1982,5 4 , 2530-2532
duration of a single step function expressing phase angle of output current (eq 7) dimensionless heterogeneous kinetic parameter (= (Do/DR)Blz,/(aDoedE/dt)1/2 (for a reduction) angular frequency linear sweep peak current function LITERATURE C I T E D Barker, 0. C. I n “Advances in Polarography”; Longmulr, 1. S., Ed.; Pergamon Press: New York, 1960; p 144. Christie, J. H.; Lingane, P. J. J. Necfroanal. Chem. 1965, 10, 176-182. Zipper, J. J.; Perone, S. P. Anal. Chem. 1973, 4 5 , 452-458. Ferrier, D. R.; Schroeder, R. R. J. Electroanal. Chem. 1973, 45, 343-359. Ferrler, D. R.; Chidester. D. H.; Schroeder. R. R. J. Electroanal. Chem. 1973, 4 5 , 361-378. Ryan, M. D. J. Electroanal. Chem. 1977, 7 9 , 105-119. Surprenant, H. L.; Ridgway, T. H.; Reiiley, C. N. J. Electroanal. Chem. 1977, 7 5 , 125-134. Miaw. L. H. L.; Boudreau, P. A,; Pichler, M. A.; Perone, S. P. Anal. Chem. 1978, 5 0 , 1988-1996.
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RECEIVED for review March 30, 1982. Accepted August 31, 1982. This work was financially supported by C.N.R. (Rome).
Exchange Current Densities and Other Properties of Reference Electrodes Based on the Triiodide-Iodide and Silver( I) Ion-Silver Couples in Organic Solvents J. F. Coetzee* and C. W. Gardner, Jr. Department of Chemlstty, Universl& of Plttsburgh, Pittsburgh, Pennsylvania 15260
Exchange current densltles measured galvanostatlcally are reported for the sliver( I ) Ion-sllver couple In propylene carbonate and acetonltrlle and for the trllodlde Ion-Iodide Ion couple at platinum In propylene carbonate, acetonltrlle, ethanol, and water, as well as at stalnless steel in propylene carbonate and acetonltrlle and at glassy carbon In acetonltrlle. Exchange current densltles are much greater for the 13-,1couple on platinum than for the Ag+/Ag couple and decrease In the order platlnum > glassy carbon > stalnless steel. Exchange current densltles are also solvent dependent. We are now recommending the followlng external reference electrode for use In organlc solvents: a double-Junctionassembly conslstlng of a Pt/( 13- I-) electrode comblned wlth a salt bridge terminated In a Teflon roll junctlon, the entire assembly Containing the same solvent as that In the analyte solutlon.
+
The selection of an appropriate reference electrode for measurements in organic solvents is a nontrivial matter. For many organic solvents, particularly aprotic solvents, internal reference electrodes are not available, for reasons indicated elsewhere ( I ) . This paper is concerned with the selection of an appropriate external reference electrode. In early work in organic solvents (2,3),aqueous external reference electrodes were usually employed; these were typically separated from the analyte solution by a salt bridge containing the same solvent as that in the analyte solution. Such arrangements have several disadvantages, however. Apart from the obvious problem that contamination of the analyte solution by leakage of water may occur unless care is exercised (2), the reproducibility of the liquid-junction 0003-2700/82/0354-2530$01.25/0
potential at the water-organic solvent interface may be no better than several millivolts; other problems may also arise (4). The result is that, in later work, most workers used external reference electrodes containing the same solvent as in the analyte solution. The reference electrode was based, overwhelmingly, on the Agt/Ag couple (3,5). We will now show that the 13-,1-couple has significant advantages for this purpose. Previous work has already shown that the 1,- ion is quite stable in most organic solvents (6)and that the I
