Detection of Nitrate(NO^-₂) Ions Produced in Disproportionation of Nitrogen(II) Oxide in Aqueous Solution

The nitrate ions (NO^-₂), products of disproportionation of NO in aqueous solution, were detected by an Orion Nitrite Electrode 97-46. Calibrations by means of standard NaNO₂ solutions within the range 0.001÷100 ppm indicated linear dependence of EMF on ppm within 1÷100 ppm. Measurements justified the usefulness of this detection method of NO in solutions of OH^- concentration lower than 10^-2 mol dm^-3 since at higher concentrations the EMF values exceeded the measurement range of the electrode. Occurrence of nitrate ions produced in the disproportionation reaction was additionally confirmed in dependence of OH^- concentration by near UV and fluorescence spectra. The calibrated ion-selective nitrate electrode has also been shown, on the basis of Co(II)-dipeptide-OH^- systems, as a useful tool in studying reversible NO uptake by Co(II) chelates in aqueous solution. Such a reaction may be regarded as simulating the harmful binding of NO by hemoglobin, where it substitutes the isoelectronic dioxygen.