Determination of Microgram Amounts of Nitrite Ion using a Tensammetric Wave of the Oxidation Product of 1-Amino-2-naphthol-4-sulfonic Acid

Abstract

1-Amino-2-naphthol-4-sulfonic acid (ANS) is polarographically inactive in the pH range from 0.8 to 12, but its oxidation product gives a sensitive A. C. wave, just as in the case of o-aminophenol. ANS is oxidized slowly with dissolved oxygen in the pH range from 1.5 to 3, whereas it is very rapidly oxidized in the presence of chromate, permanganate and nitrite ion in the same pH range. Therefore, the sensitive A. C. wave of the oxidation producut of ANS was utilized for the determination of microgram amounts of nitrite ion.
Drop time curves, temperature coefficients of the A. C. wave height and the D. C. wave height at potentials where the A. C. wave occurs indicates that the A. C. wave has a tensammetric nature. The infrared spectra, NMR spectra and ultimate analysis of the oxidation product of ANS supports that ANS is oxidized with nitrite ion according to equation 1.
The optimum conditions for the determination of nitrite ion were as follows: poassium hydrogen phthalate-HCl0₄ buffer: 0.025 mol/l, ANS: 2 x 10^-4 mol/l, standing time: 40 minutes, pH: 2.0, temperature: 50° C. A linear calibration curve was obtained over the concentration range between 0.03 and 0.3, ug/ml of nitrite ion with good reproducibility. Mo (VI), W (VI), Cr (la), S0₃^2- and Fe (III) interfere, but a small amounts of Al(III), Bi (III), Cu (II), Hg (II), Ag(I), Cl0₄^-, NH₄⁺ and some of organic substances such as amino acid, starch, methanol and nonionic detergent which shows interference with Griess-Romijin method do not cause interference with this method.