title: A comprehensive structural evaluation of humic substances using several fluorescence techniques before and after ozonation. Part II: evaluation of structural changes following ozonation.
abstract: The main objective of this work (Part II) is to evaluate the usefulness of fluorescence techniques to monitor structural changes in humic substances produced by the ozonation treatment, using all the current fluorescence techniques: Emission scan fluorescence (ESF), synchronous fluorescence spectroscopy (SFS), total luminescence spectroscopy (TLS or EEM) through the use of both 2-D contour maps and 3-D plots, fluorescence index and the λ0.5 parameter. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard: SUFA, Suwannee River Humic Acid Standard: SUHA and Nordic Reservoir Fulvic Acid Reference: NOFA) and the other one was a commercial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: ALHA). The lowest ozone dosage tested (0.25mg O3/mg TOC) caused no appreciable change in the different types of fluorescence spectra under study, therefore the structural change produced in the humic macromolecules may be considered of little significance. Concerning EEM and synchronous spectra, the two natural fulvic acids (SUFA and NOFA) showed a decrease in fluorescence intensity as ozone dosage increased, but the natural humic acid (SUHA) showed a different behaviour: an initial increase in fluorescence intensity at medium ozone dosages (1.5 mg O3/mg TOC) followed by an intensity decrease for the higher ozone dose (7.5 mg O3/mg TOC). Regarding synchronous spectra, the moderate dosage of 1.5 mg O3/mg TOC led to an increase in the fluorescence of the protein-like peak at λsyn=285 nm for the natural humic substances. The results obtained for the fluorescence index and λ0.5 may suggest that the greatest degradation of aromatic structures within the humic macromolecule occurs at high ozone dosages, whereas the predominant effect at moderate dosages would be the break-up of the humic macromolecule into lower molecular weight fragments. The behaviour of the commercial humic acid (ALHA) upon ozonation was very different from that of the natural humic substances (SUFA, SUHA and NOFA), a result that was confirmed with all the fluorescence techniques used in this study and that would cast doubt on the use of commercial humic acids as surrogates for natural humic substances.
authors.affiliation: Department of Chemistry, Higher Polytechnic School, University of Burgos, Av. Cantabria s/n, 09006 Burgos, Spain. Electronic address: qpvito@ubu.es.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Rodríguez
authors.affiliation: Department of Chemistry & Biology, Faculty of Mathematics and Natural Science, University of Wuppertal, Germany. Electronic address: patrick.schlenger@googlemail.com.
authors.forename: Patrick
authors.initials: P
authors.lastname: Schlenger
authors.affiliation: Department of Chemistry, Faculty of Sciences, University of Burgos, Pz. Misael Bañuelos s/n, 09001 Burgos, Spain. Electronic address: magaval@ubu.es.
authors.forename: María
authors.initials: M
authors.lastname: García-Valverde
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D015394:Molecular Structure; D010126:Ozone / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D014874:Water Pollutants, Chemical; D010126:Ozone; C005023:fulvic acid
keywords: Emission scan fluorescence; Fluorescence index; Humic substances; Ozonation; Synchronous fluorescence spectroscopy; Total luminescence spectroscopy