Electrospray ionization mass spectrometry monitoring of indigo carmine degradation by advanced oxidative processes.
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-1H-indole-5-sulfonic acid (3, m/z 226), 2-amino-alpha-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.
Dalmázio
Ilza
I
Department of Chemistry, Federal University of Minas Gerais, Belo Horizonte, MG 31270-901, Brazil.
de Urzedo
Ana P F M
AP
Alves
Tania M A
TM
Catharino
Rodrigo R
RR
Eberlin
Marcos N
MN
Nascentes
Clésia C
CC
Augusti
Rodinei
R
D004396:Coloring Agents / Q000032:analysis* / Q000737:chemistry; D006861:Hydrogen Peroxide; D007203:Indigo Carmine / Q000032:analysis* / Q000737:chemistry; D007454:Iodides; D010084:Oxidation-Reduction; D010126:Ozone; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry
D004396:Coloring Agents; D007454:Iodides; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D010126:Ozone; D006861:Hydrogen Peroxide; D007203:Indigo Carmine