Polarograms were recorded on a Sargent model XVI polarograph. Waterjacketed three-compartment cells maintained at 25ยฐC_+0.1ยฐC and containing a saturated calomel electrode (SCE) and a platinum counterelectrode in saturated KC1 solution were employed. All potentials are referred to the SCE at 25ยฐC.
The dropping mercury electrode had normal m and t values. Triple-distilled mercury was used for all coulometric and polarographic studies.
Cyclic voltammetry was performed with the apparatus described by Dryhurst et al. 2 Voltammograms were recorded on a Moseley model 7001A X-Y recorder.
Controlled-potential electrolyses were performed with a unit based on operational amplifier circuits 3. Current integration during electrolysis utilized an Anadex d.c. to frequency converter and a high-sensitivity digital electronic counter. Current flowing through the working electrode was measured in terms of the voltage drop across a standard resistor.
Ultraviolet adsorption spectra were obtained with a Perkin Elmer-Hitachi model 124 spectrophotometer using 1.00 cm stoppered quartz cells.
The preparation of the pyrolytic graphite electrode (PGE) has been described earlier 4.
The three-compartment macroscale electrolysis cell employed a mercury pool working electrode (area ~ 33.2 cm2), a platinum gauze counterelectrode, and a SCE reference electrode. A gas-dispersion tube was sealed into the working electrode compartment through which a stream of argon was continuously bubbled. A platinum wire furnished electrical contact with the mercury pool. A three-compartment water--0.54 -0.68 -0.81 ยข -0.