Estimation of Nitrite Ions by the Formation of Aryl Nitroanion Radicals in the Reaction with the Aminoarene 3,5-Dibromo-4-Amino-Benzenesulfonic Acid by EPR Spectroscopy. The Use of 15N-Nitrite as an Internal Standard

The reaction between the aminoarene 3,5-dibromo-4-aminobenzenesulfonic acid (Na-salt) and nitrite ions gives rise to the corresponding nitroanion radical. In the reaction the amino group of the parent substance was replaced by NO2 from the nitrite ions. This leads to two different EPR spectra when the reaction was made with 14N and 15N nitrite. Furthermore, the two spectra were completely separated with no overlaps, a property which was utilised for a quantitative evaluation of samples of 14N nitrite by means of the addition of a known amount of 15N nitrite as an internal standard. Variation of the concentration of the nitroanion radicals was eliminated since the variation will affect the 14N and 15N products to the same extent. The amplitudes of the spectral components MI = +1 of the 14N spectrum and MI = +image of the 15N spectrum were used for the evaluation of the 14N nitrite content of the sample.