A rotating ring (platinum)-disk (graphite) electrode is employed to analyze CO2 in aqueous solutions. A graphite disk, coated with the complex N,N’,N ",N"’-tetramethyltetra-3,4-pyridoporphyrazinocobalt(II) and protected by a Nafion(R) film, displays electrocatalytic activity toward CO2 reduction. The carbon monoxide generated can be thrown on to the platinum ring electrode where it is adsorbed and can be detected by its electrochemical oxidation. The CO oxidation current at the ring electrode is dependent on the CO2 concentration and the disk electrode potential. Although, as with most other catalysts, proton reduction also occurs, this does not interfere with the analysis procedure.