Influence of Reagent Concentration and Reaction Rate on Colorimetry of Nitrite Ion by Saltman Method

Abstract

Concerning the colorimetry of nitrite ion induced to azo dye, the influence of the ratio between sulfanilic acid or sulfanilamide and N-(1-naphthyl)etylenediamine and the kinetics for the diazotization and coupling reaction are discussed. The sensitivity of a stepwise method is 23% higher than that using a Saltzmann reagent which is mixture of sulfanilic acid, N-(1-naphtyl)etylenediamine and phosphoric acid. The same sensitivity is 41% higher by using sulfanilamide instead of sulfanilic acid. The diazotization and coupling reaction are second-order reaction. That is, R = k[sulfanilic acid or sulfanilamide][nitrite ion] and R = k[diazonium ion][N-(1-naphthyl)etylenediamine] respectively. The coupling reaction rate is about 10-times faster than the diazotization.