Electrospray ionization mass spectrometry monitoring of indigo carmine degradation by advanced oxidative processes

✍ Scribed by Ilza Dalmázio; Ana P. F. M. de Urzedo; Tania M. A. Alves; Rodrigo R. Catharino; Marcos N. Eberlin; Clésia C. Nascentes; Rodinei Augusti

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 176 KB
• Volume: 42
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1159

✦ Synopsis

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 CC 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.