探针电喷雾电离质谱技术实时原位监测土霉素光催化降解

Study on the Photocatalytic Degradation of Oxytetracycline by Probe Electrospray Ionization Mass Spectrometry

探针电喷雾电离质谱(PESI-MS)是一种适用于直接分析复杂体系,并能够提供较高时间分辨率的原位技术,可原位监测各种反应。鉴于四环素类抗生素滥用引发的环境污染问题,本文利用PESI-MS技术对紫外光照下TiO_(2)光催化土霉素降解进行了160 min的连续实时原位监测分析。结果表明,土霉素分子离子强度随反应的进行逐渐降低,生成多种降解产物,通过分析所得的时间分辨谱图,获得了35种主要的降解产物。根据各降解产物的提取离子流图变化情况,筛选出7个主要的降解产物,并推测出10条可能的降解路径,其中只有2条降解路径可将土霉素降解至相对分子质量较低的产物。该结果可为光催化反应的动力学研究和新型光催化剂的开发提供数据参考,以更全面地了解光催化反应机理。

The abuse of antibiotics has caused severe environmental issues.Photocatalytic treatment technology has the advantages of high efficiency,strong effectiveness and no secondary pollution,which presents great potential for degrading or removing many kinds of environment pollutants.However,the intermediate products formed during the photocatalytic degradation process of antibiotics may possess greater toxicity than the antibiotics themselves,and the toxicity of most of these intermediates still remains unclear.Therefore,understanding the photocatalytic degradation pathways of antibiotics and obtaining qualitative and quantitative information about the main degradation products are of vital importance for the large-scale application of photocatalytic technology in the removal of antibiotics and other pollutants.Probe electrospray ionization mass spectrometry(PESI-MS)technology,adopting a solid probe as the electrospray ionization emitter,has the advantages of rapid response,low sample consumption,high salt tolerance,and strong resistance to suspended particles.These features make PESI-MS to be an ideal technique for direct analysis of complex systems,such as biological and chemical reactions.In this study,PESI-MS was used to perform continuous real-time in situ monitoring and analysis of the photocatalytic degradation of oxytetracycline(OTC),which photocatalyzed by TiO2 under UV irradiation for 160 min,with spectra collected at a resolution of 1 spectrum per second.The results showed that the intensity of protonated OTC ions decreases progressively during the reaction,and forms product ions at various stages of degradation.35 Kinds of key degradation products are identified by high time-resolved spectra.Based on the changes in the extracted ion chromatograms(EIC)of these products,7 major degradation products are screened out and 10 possible degradation pathways are proposed,two of which can lead to the degradation of OTC into lower molecular weight products.Although complete photocatalytic degradation of OTC is not achieved in the experimental conditions,the amount of degradation products observed in this study is significantly higher than those previously reported using various high performance liquid chromatography mass spectrometry(HPLC-MS).Furthermore,in the early stages of the photocatalytic process,products of combined ethyl radicals and ethoxy radicals are detected,which likely are contributed by the ethanol added intentionally in the reaction.The use of organic solvents to reduce solution surface tension during PESI operation at atmospheric pressure is inevitable.In the future,we aim to develop a high-pressure PESI ionization source to resolve this issue,which is expected to reveal a more accurate photocatalytic reaction mechanism and pathway.The findings of this study provide valuable data for understanding the kinetics of photocatalytic reactions and developing new photocatalysts,helping researchers gain a more comprehensive understanding of photocatalytic mechanisms.