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

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-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.

Improving the Indigo Carmine Decolorization Ability of a Bacillus amyloliquefaciens Laccase by Site-Directed Mutagenesis

“…The m/z peak at 226 is a characteristic peak of ISA, which can be further converted to the anion of m/z 244 by the addition of H 2 O. Both products of m/z 226 and 244 can be identified during indigo carmine degradation by other methods [32][33][34]. These results are consistent with that of the UV-visible spectra, which revealed the characteristic peak of ISA at 235 nm.…”

Degradation of food dyes by zero-valent metals exposed to ultrasonic irradiation in water medium: optimization and electrospray ionization mass spectrometry monitoring

“…30 Recent examples have shown that ESI-MS, in conjunction with ESI-MS/MS, can be successfully applied to monitor a number of processes, including the environmentally-relevant ones, furnishing novel and significant information about them. [31][32][33][34][35][36][37][38][39][40][41] In this work, ESI(-)-MS (electrospray ionization mass spectrometry in the negative ion mode), in conjunction with ultraviolet-visible spectrophotometry (UV-Vis) and total organic carbon (TOC) techniques, were employed to monitor the reductive degradation of four prototype food dyes: Amaranth (1), Sunset Yellow (2), Red 40 (3) and Brilliant Blue (4) (Figure 1). The reactions were Figure 1.…”

The Role of Pulse Voltage Amplitude on Chemical Processes Induced by Streamer Discharge at Water Surface

“…Indigo carmine (C18H8N2Na2O8S2) consists of a chromogenic bond of a single C=C double bond substituted by two NH donor groups, with two C=O acceptor groups at the center of the formula [16,24,[33][34][35]. The unsaturated bond is a double bond of carbon in a benzene ring, and the center of the formula of indigo carmine [23,24].…”

“…These results indicate that the strong chromogenic C=C double bond, which is mainly responsible for the blue color of dye solution, is To confirm the results and clarify the role of voltage amplitude on water surface streamer discharge, we treated an Indigo carmine (IC) organic dye solution as a polluted water sample. Indigo carmine (C 18 H 8 N 2 Na 2 O 8 S 2 ) consists of a chromogenic bond of a single C=C double bond substituted by two NH donor groups, with two C=O acceptor groups at the center of the formula [16,24,[33][34][35]. The unsaturated bond is a double bond of carbon in a benzene ring, and the center of the formula of indigo carmine [23,24].…”