The thermodynamic properties of some commonly used oxidation-reduction mediators, inhibitors and dyes, as determined by polarography.

The oxidation-reduction midpoint potentials (Em) of the following compounds have been measured in the range of pH from 3 to 12 by polarography: methyl viologen; benzyl viologen; 2-hydroxy-1,4-naphthoquinone; 2-hydroxy-1,4-anthraquinone; N,N,N',N',-tetramethyl-p-phenylenediamine; 2,3,5,6-tetramethyl-p-phenylenediamine; phenazine; N-methylphenazonium methosulfate; N-methylphenazonium sulfonate methosulfate; N-ethylphenazonium ethosulfate; pyocyanine; neutral red; safranin; phenol red; chlorophenol red; cresol red; bromocresol purple; 2,5-dibromo-3-methyl-6-isopropylbenzoquinone and 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole. Many of these previously assumed to have a simple behavior in this range have proven to be rather more complicated, and several anomalous observations have been reconciled.