title: Dependence of transformation product formation on pH during photolytic and photocatalytic degradation of ciprofloxacin.
abstract: Ciprofloxacin (CIP) is a broad-spectrum antibiotic with five pH dependent species in aqueous medium, which makes its degradation behavior difficult to predict. For the identification of transformation products and prediction of degradation mechanisms, a new experimental concept making use of isotopically labeled compounds together with high resolution mass spectrometry was successfully established. The utilization of deuterated ciprofloxacin (CIP-d8) facilitated the prediction of three different degradation pathways and the corresponding degradation products, four of which were identified for the first time. Moreover, two molecular structures of previously reported transformation products were revised according to the mass spectra and product ion spectra of the deuterated transformation products. Altogether, 18 transformation products have been identified during the photolytic and photocatalytic reactions at different pH values (3, 5, 7 and 9). In this work the influence of pH on both reaction kinetics and degradation mechanism was investigated for direct ultraviolet photolysis (UV-C irradiation) and photocatalysis (TiO2/UV-C). It could be shown that the removal rates strongly depended on pH with highest removal rates at pH 9. A comparison with those at pH 3 clearly indicated that under acidic conditions ciprofloxacin cannot be easily excited by UV irradiation. We could confirm that the first reaction step for both oxidative treatment processes is mainly defluorination, followed by degradation at the piperazine ring of CIP.
authors.affiliation: Institut für Energie- und Umwelttechnik e. V. (IUTA, Institute of Energy and Environmental Technology), Bliersheimer Straße 58-60, 47229 Duisburg, Germany.
authors.forename: Alaa
authors.initials: A
authors.lastname: Salma
authors.affiliation: University Hospital Aachen, Institute for Hygiene and Environmental Medicine, Pauwelsstraße 30, 52074 Aachen, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Thoröe-Boveleth
authors.affiliation: University Duisburg-Essen, Faculty of Chemistry, Instrumental Analytical Chemistry, Universitätsstraße 5, 45141 Essen, Germany; Centre for Water and Environmental Research (ZWU), University Duisburg-Essen, Universitätsstraße 2, 45141 Essen, Germany.
authors.forename: Torsten C
authors.initials: TC
authors.lastname: Schmidt
authors.affiliation: Institut für Energie- und Umwelttechnik e. V. (IUTA, Institute of Energy and Environmental Technology), Bliersheimer Straße 58-60, 47229 Duisburg, Germany; Centre for Water and Environmental Research (ZWU), University Duisburg-Essen, Universitätsstraße 2, 45141 Essen, Germany. Electronic address: tuerk@iuta.de.
authors.forename: Jochen
authors.initials: J
authors.lastname: Tuerk
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002939:Ciprofloxacin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010782:Photolysis; D014025:Titanium; D014466:Ultraviolet Rays
chemical_list: D000900:Anti-Bacterial Agents; C009495:titanium dioxide; D002939:Ciprofloxacin; D014025:Titanium
keywords: Ciprofloxacin; Photocatalytic degradation; Photolysis; Transformation products