Amperometric detection of NO and NO_2 in the ppb range with solid-polymer electrolyte membrane supported noble metal electrodes

摘要

NO and NO_2 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 NO_2 at the two electrodes, the concentration of each analyte in a mixture of hte gases can be determined. The detection limits (S/N=3,n=5) for NO and NO_2 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 SO_2 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 SO_2 is more than 10-times lower compared to a cell with 0.5 M sulfuric acid, while the sensitivites for NO and NO_2 are almost identical for both acid concentrations.