Ion-exchange voltammetry of tris(2,2′-bipyridyl) ruthenium(II), iron(II), osmium(II) and tris(2,2′-bipyrazyl) ruthenium(II) in acetonitrile solutions at poly(ester-sulphonate) coated electrodes

Abstract

Glassy carbon electrodes modified with the poly(ester-sulphonate) ionomer Kodak AQ 55 D are used and characterized in acetonitrile solutions. The potential window accessible in acetonitrile + tetrabutylammonium hexafluorophosphate extends from −1.750 V to +1.900 V vs. an aqueous KCl saturated Ag/vbAgCl reference electrode. The electrochemical behaviour of [Ru(bpy) 3] 2+, [Fe(bpy) 3] 2+, [Os(bpy) 3] 2+ and [Ru(bpz) 3] 2+ (where bpy = 2,2′bipyridyl and bpz = 2,2′bipyrazyl) is studied at the modified electrode. All the electroactive cations are preconcentrated efficiently in the polymeric coating. In the case of bpy complexes both a one-electron oxidation as well as two one-electron steps of the stepwise reduction of the starting complex are detected at the modified electrode. In the case of [Ru(bpz) 3] 2+, three consecutive reduction steps can be observed, while no oxidation process is observed in the direct positive scan before reaching the upper limit of the potential range accessible at the modified electrode. The relative order in the ion-exchange selectivity coefficients in acetonitrile solutions for the cations studied is evaluated by comparison with the electrochemical behaviour observed at unmodified electrodes. The possibility of gaining information on preconcentration effects for ion-exchange voltammetry in non-aqueous solvents from the Gibbs energies of transfer from water to hydrophobic media is also discussed.