title: Advanced oxidation of caffeine in water: on-line and real-time monitoring by electrospray ionization mass spectrometry.
abstract: High performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV), and total organic carbon (TOC) analyses show that caffeine is quickly and completely degraded underthe oxidative conditions of the UV/H2O2,TiO2/ UV, and Fenton systems but that the organic carbon content of the solution decreases much more slowly. Continuous on-line and real-time monitoring by electrospray ionization mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS) as well as high accuracy MS measurements and gas chromatography-mass spectrometry analysis show that caffeine is first oxidized to N-dimethylparabanic acid likely via initial OH insertion to the C4=C8 caffeine double bond. A second degradation intermediate, di(N-hidroxymethyl)parabanic acid, has been identified by ESI-MS and characterized by ESI-MS/MS and high accuracy mass measurements. This polar and likely relatively unstable compound, which is not detected by off-line GC-MS analysis, is likely formed via further oxidation of N-dimethylparabanic acid at both of its N-methyl groups and constitutes an unprecedented intermediate in the degradation of caffeine.
authors.affiliation: Chemistry Department, Federal University of Minas Gerais-UFMG, Belo Horizonte, MG 31270-901, Brazil.
authors.forename: Ilza
authors.initials: I
authors.lastname: Dalmázio
authors.forename: Leonardo S
authors.initials: LS
authors.lastname: Santos
authors.forename: Renata P
authors.initials: RP
authors.lastname: Lopes
authors.forename: Marcos N
authors.initials: MN
authors.lastname: Eberlin
authors.forename: Rodinei
authors.initials: R
authors.lastname: Augusti
mesh_terms: D001331:Automation; D002110:Caffeine / Q000032:analysis / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004784:Environmental Monitoring / Q000379:methods; D008401:Gas Chromatography-Mass Spectrometry; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D012984:Software; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D002110:Caffeine