Oxidative Degradation of Indigocarmine by Hypochlorite—A Tool for Determination of Hypochlorite in Commercial Samples

Abstract

The oxidative action of hypochlorite on indigocarmine is investigated. Hypochlorite dissociates indigocarmine to produce isatin-5-monosulphonic acid, with a stoichiometry of 2:1. The probable mechanism is proposed. The suitability of reaction between hypochlorite and indigocarmine as an indicator reaction for the determination of high levels of hypochlorite in synthetic and commercial samples is investigated. A simple and reliable kinetic-analytical method is developed for the determination of hypochlorite ion at alkaline pH, based on its oxidizing activity.

Kinetics and mechanism of the oxidation of Coomassie Brilliant Blue-R dye by hypochlorite and role of acid therein

“…10 We have also reported the oxidation kinetics and mechanisms of reactions of triaryl 11,12 (aniline blue and thymol blue), phenothiazine 13 (methylene blue) and heterocyclic 14,15 (acridine orange and safranine-o) dyes with acidic bromate as oxidant. We also investigated the oxidative degradation kinetics of indigo carmine with hypochlorite 16 and the reaction kinetics of triaryl 17 (methylene violet), benzophenoxazines 18 (Nile blue and Meldola's blue) and phenothiazine 19 (toluidine blue) dyes with chlorite under low pH conditions. More recently, we investigated and reported the kinetics and mechanism of oxidation of the toxic dye, amaranth, by hypochlorite and hypochlorous acid under varied pH conditions.…”

Superoxide Converts Indigo Carmine to Isatin Sulfonic Acid

“…Ozone reacts rapidly with indigo carmine (18). Other oxidants, including hypochlorous acid and singlet oxygen also bleach this blue dye (4,19). However, with ozone but not the other oxidants, an atom of oxygen from water was found to be incorporated into isatin sulfonic acid (4), as in Scheme 1.…”