Identification of metol degradation products under Fenton’s reagent treatment using liquid chromatography-mass spectrometry

Many aromatic compounds are oxidized but not completely mineralized by Fenton’s reagent. Little attention has so far been given to the identification of residual organic matter and the evaluation of its toxicity. In this work, the oxidation of metol [N-methyl-p-aminophenol] by Fe2+/H2O2 in the dark as a model for aromatic amines and alcohols was examined. Analysis of oxidized solutions was performed by both LC-electron impact (EI)-MS and LC-electrospray ionization (ESI)-MS. It was checked that the degradation of metol takes place via direct oxidation by Fe3+ and OH√ attack. Intermediates amenable to oxidation by OH√ are basically partially oxygenated aromatic species, dimerization products and polymers. End products not amenable to oxidation by this radical are ferrycarboxylate complexes, which are non-toxic to UC581 bacterial cells. These complexes can be completely destroyed by irradiation with light. The photo-Fenton reaction is therefore an effective choice for the in situ treatment of industrial effluents containing aromatic amines and hydroxylated species.