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Electrospray ionization mass spectrometry monitoring of indigo carmine degradation by advanced oxidative processes
Author(s) -
Dalmázio Ilza,
de Urzedo Ana P. F. M.,
Alves Tania M. A.,
Catharino Rodrigo R.,
Eberlin Marcos N.,
Nascentes Clésia C.,
Augusti Rodinei
Publication year - 2007
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1159
Subject(s) - chemistry , indigo carmine , mass spectrometry , electrospray ionization , chromatography , electrospray , nuclear chemistry
Abstract The degradation of the dye indigo carmine in aqueous solution induced by two oxidative processes (H 2 O 2 /iodide and O 3 ) was investigated. The reactions were monitored by electrospray ionization mass spectrometry in the negative ion mode, ESI(−)‐MS, and the intermediates and oxidation products characterized by ESI(−)‐MS/MS. Both oxidative systems showed to be highly efficient in removing the color of the dye aqueous solutions. In the ESI(−)‐MS of the indigo carmine solution treated with H 2 O 2 and H 2 O 2 /iodide, the presence of the ions of m / z 210 (indigo carmine in its anionic form, 1), 216, 226, 235, and 244 was noticeable. The anion of m / z 235 was proposed to be the unprecedented hydroperoxide intermediate 2 formed in solution via an electrophilic attack by hydroxyl and hydroperoxyl radicals of the exocyclic CC bond of 1. This intermediate was suggested to be rapidly converted into the anionic forms of 2,3‐dioxo‐1 H ‐indole‐5‐sulfonic acid (3, m / z 226), 2‐amino‐α‐oxo‐5‐sulfo‐benzeneacetic acid (4, m / z 244), and 2‐amino‐5‐sulfo‐benzoic acid (5, m / z 216). In the ESI(−)‐MS of the indigo carmine solution treated with O 3 , two main anions were detected: m / z 216 (5) and 244 (4). Both products were proposed to be produced via an unstable ozonide intermediate. Other anions in this ESI(−) mass spectrum were attributed to be [4 − H + Na] − of m / z 266, [4 − H] 2− of m / z 121.5, and [5 − H] 2− of m / z 107.5. ESI‐MS/MS data were consistent with the proposed structures for the anionic products 2–5. Copyright © 2007 John Wiley & Sons, Ltd.