Dalmázio Ilza, Santos Leonardo S, Lopes Renata P, Eberlin Marcos N, Augusti Rodinei
Chemistry Department, Federal University of Minas Gerais-UFMG, Belo Horizonte, MG 31270-901, Brazil.
Environ Sci Technol. 2005 Aug 15;39(16):5982-8. doi: 10.1021/es047985v.
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.
高效液相色谱法（HPLC）、紫外光谱法（UV）和总有机碳（TOC）分析表明，在UV/H2O2、TiO2/UV和芬顿体系的氧化条件下，咖啡因能迅速且完全降解，但溶液中的有机碳含量下降得要慢得多。通过电喷雾电离质谱（ESI-MS）和串联质谱实验（ESI-MS/MS）进行的连续在线实时监测，以及高精度质谱测量和气相色谱-质谱分析表明，咖啡因首先可能通过最初的OH插入到C4=C8咖啡因双键上而被氧化为N-二甲基仲班酸。通过ESI-MS鉴定出了第二种降解中间体二（N-羟甲基）仲班酸，并通过ESI-MS/MS和高精度质谱测量对其进行了表征。这种极性且可能相对不稳定的化合物，离线GC-MS分析未检测到，它可能是由N-二甲基仲班酸的两个N-甲基进一步氧化形成的，是咖啡因降解过程中一种前所未有的中间体。
