title: Degradation of caffeine and identification of the transformation products generated by ozonation.
abstract: The ozonation of caffeine in water was performed at different pH values, including acidic conditions. Kinetic experiments were conducted by adding pulses of a concentrated caffeine solution to ozone saturated water. The results showed a rapid decrease of ozone concentration during the first 15s after injection, followed by a gradual decline at a much slower rate. The data were fitted to a second order kinetic model with rate constants increasing from 0.25 to 1.05 M(-1)s(-1) for pH in the 3-10 range. The initial ozone consumption per mol of ozonated caffeine was greater at high pH values, reflecting a higher ozone decomposition rate. The decomposition of ozone was positively affected by the concentration of caffeine, an effect that could be attributed to the presence of a reaction intermediate from the ozonation of caffeine that behaved as a strong promoter of ozone decomposition. A study of the transformation products identified by liquid chromatography in combination with time-of-flight mass spectrometry was carried out, which permitted a tentative degradation pathway to be proposed and several persistent by-products to be identified at both pH 3 and 8. Most transformation products were the result of the opening of the imidazole ring after breaking caffeine's N9C8 double bond.
authors.affiliation: Department of Chemical Engineering, University of Alcalá, 28771 Alcalá de Henares, Spain. roberto.rosal@uah.es
authors.forename: Roberto
authors.initials: R
authors.lastname: Rosal
authors.forename: Antonio
authors.initials: A
authors.lastname: Rodríguez
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Perdigón-Melón
authors.forename: Alice
authors.initials: A
authors.lastname: Petre
authors.forename: Eloy
authors.initials: E
authors.lastname: García-Calvo
authors.forename: María José
authors.initials: MJ
authors.lastname: Gómez
authors.forename: Ana
authors.initials: A
authors.lastname: Agüera
authors.forename: Amadeo R
authors.initials: AR
authors.lastname: Fernández-Alba
mesh_terms: D002110:Caffeine / Q000737:chemistry*; D002853:Chromatography, Liquid; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D002110:Caffeine; D010126:Ozone