Selective determination of oxalate with a ruthenium(II) complex/nafion-modified electrode combined with a carbon dioxide sensor

A tris(2,2'-bipyridine)ruthenium(II)/Nafion-modified Pt gauze electrode, where CO 2 was generated by oxidation of substrates, was combined with a CO 2 sensor. The combined sensor responded most effectively to oxalate among the organic acids examined. The response to oxalate was enhanced by use of a doubly-piled, modified Pt gauze electrode. The most suitable applied potential was +0.95 V vs. Ag/AgCl; the stationary response was attained in 10 min after the potential application. The response to 0.5 mM oxalate was reproducible within 3% on 10 repeated runs and remained virtually unchanged over 10 days. The calibration curve for oxalate was linear in the concentration range of 0.1 to 5 mM, and the detection limit was 0.05 mM (S/N=3)