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 electrod e, where CO2 was generated by oxidation of substrates, was combined wi th a CO2 sensor. The combined sensor responded most effectively to oxa late among the organic acids examined. The response to oxalate was enh anced by use of a doubly-piled, modified Pt gauze electrode. The most suitable applied potential was +0.95 V vs. Ag/AgCl; the stationary res ponse was attained in 10 min after the potential application. The resp onse to 0.5 mM oxalate was reproducible within 3% on 10 repeated runs and remained virtually unchanged over 10 days. The calibration curve f or oxalate was linear in the concentration range of 0. 1 to 5 mM, and the detection limit was 0.05 mM (S/N=3).