Amperometric detection of NO and NO2 in the ppb range with solid-polymer electrolyte membrane supported noble metal electrodes Original Research Article

NO and NO2 can be detected amperometrically on both gold and platinum electrodes deposited on SPE membranes in contact with sulfuric acid. The two analytes are oxidized at +700 mV versus MSE in the double layer region of a gold electrode and in the oxide region in the case of a platinum electrode. Due to different sensitivity ratios for NO and NO2 at the two electrodes, the concentration of each analyte in a mixture of the gases can be determined. The detection limits (S/N=3, n=5) for NO and NO2 were found to be 1.2 ppb (v/v) and 3.8 ppb on a Au-Nafion electrode and 22 ppb (v/v) and 17 ppb on a Pt-Nafion electrode, respectively. The well-known interference by SO2 could be suppressed significantly by using a concentration of sulfuric acid of 10 M. At this high concentration of the acid, the cross sensitivity to SO2 is more than 10-times lower compared to a cell with 0.5 M sulfuric acid, while the sensitivities for NO and NO2 are almost identical for both acid concentrations.