Rosal Roberto, Rodríguez Antonio, Perdigón-Melón José Antonio, Petre Alice, García-Calvo Eloy, Gómez María José, Agüera Ana, Fernández-Alba Amadeo R
Department of Chemical Engineering, University of Alcalá, 28771 Alcalá de Henares, Spain.
Chemosphere. 2009 Feb;74(6):825-31. doi: 10.1016/j.chemosphere.2008.10.010. Epub 2008 Nov 25.
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.
在不同pH值（包括酸性条件）下对水中的咖啡因进行臭氧化处理。通过向臭氧饱和水中添加浓缩咖啡因溶液脉冲来进行动力学实验。结果表明，注入后最初15秒内臭氧浓度迅速下降，随后以慢得多的速率逐渐下降。数据拟合到二级动力学模型，在pH值为3 - 10范围内，速率常数从0.25增加到1.05 M⁻¹s⁻¹。每摩尔臭氧化咖啡因的初始臭氧消耗量在高pH值时更大，这反映了更高的臭氧分解速率。臭氧的分解受到咖啡因浓度的正向影响，这种影响可归因于咖啡因臭氧化反应中间体的存在，该中间体表现为臭氧分解的强促进剂。开展了一项结合液相色谱与飞行时间质谱对转化产物进行鉴定的研究，这使得能够提出一个初步的降解途径，并在pH值为3和8时鉴定出几种持久性副产物。大多数转化产物是咖啡因的N9C8双键断裂后咪唑环开环的结果。
