溶液pH值对二嗪磷紫外光降解产物及降解途径的影响

doi:10.6023/A15070520

摘要/Abstract

在低压汞灯(253.7 nm)光照条件下, 研究了溶液pH值对农药二嗪磷光降解产物及降解途径的影响. 结果表明: 不同溶液pH值条件下二嗪磷的光降解均符合一级反应动力学, 其在中性(pH=7.0, k=0.0234 min^-1)和碱性(pH=10.0, k=0.0236 min^-1)条件下的光降解速率基本相同, 且略高于酸性(pH=4.0, k=0.0193 min^-1)时的光降解速率. 通过UPLC-ESI-MS/MS对降解产物测定分析发现: 溶液pH值显著地影响了二嗪磷光降解产物的种类及生成量. 溶液pH=4.0、7.0和10.0的二嗪磷溶液分别UV光照60 min时分别检出了五种、八种和六种主要的光降解产物, 且同一产物在不同pH值条件下的生成量存在显著差异. 结合MS和MS/MS质谱图信息, 推导出了二嗪磷主要光降解产物的分子结构, 并根据光降解产物种类及生成量随光照时间的变化关系提出了不同溶液pH值时二嗪磷的可能降解途径.

关键词: 二嗪磷, pH, 紫外光, 光解产物, 降解途径

The direct photolysis of an organophosphorus pesticide, diazinon, was investigated under monochromatic ultraviolet (UV) irradiation (253.7 nm) at different solution pH. Photolysis was conducted in an annular photochemical reactor, in the axis of which a low-pressure mercury UV lamp was installed. The photon flux into the solution from the UV lamp was determined to be at 1.18×10^-7 Einstein·s^-1. A magnetic stirrer was located at the bottom of the reactor to maintain homogeneity of the reacting solution. A thermostatic water recirculation system was used to control the solution temperature at 20±0.5 ℃. Prior to photolysis, the UV lamp was ignited for 30 min for a stable output. UV photolysis was performed with ultrapure water containing an initial 5 mg/L diazinon. Solution pH (4.0, 7.0 and 10.0) was buffered using 2 mmol/L phosphate and/or borate buffers. The analyses of diazinon and its UV photo-degradation intermediates were conducted by using ultra-performance liquid chromatography-electrospray-tandem mass spectrometry (UPLC-ESI-MS/MS) coupled with an ACQUITY^TM UPLC BEH C8 separation column. Full-scan spectra were acquired from 50 to 500 m/z in both positive electrospray ionization (ESI+) mode and negative electrospray ionization (ESI-) mode. To obtain further information for analyzing the structure of UV photo-degradation intermediates of diazinon, collision induced dissociation (CID) experiments were also conducted. The collision energy for each intermediate was optimized in the range from 15 to 35 eV. Argon was used as collision gas and its flow rate was at 0.12 mL/min. The results show that solution pH affected significantly on the photo-degradation rate of diazinon. The rate was lower at acidic pH 4 (the pseudo-first-order rate constant (k) is 0.0193 min^-1) than those at neutral and alkaline pH values of 7.0 and 10.0 (k=0.0234 min^-1 and k=0.0236 min^-1, respectively). More than 90% of diazinon were degraded within 120 minutes of UV irradiation at all the three pH values. The photolysis intermediates of diazinon were found to vary with solution pH. There are 5, 8, and 6 major species of photolysis intermediates for diazinon after 60 minutes of UV irradiation in water at pH of 4.0, 7.0 and 10.0, respectively. Moreover, the amount of a certain intermediate formed was very different under different pH conditions. A systematic qualitative and quantitative analyses of the photo-degradation intermediates of diazinon under different pH conditions were conducted. The molecular structure of the intermediates were deduced based on the information of mass spectrometry; the photo-degradation pathways of diazinon under different pH conditions were also proposed.

Key words: diazinon, pH, ultraviolet, photolysis intermediates, degradation pathway

引用此文

刘玉灿, 段晋明, 李伟. 溶液pH值对二嗪磷紫外光降解产物及降解途径的影响[J]. 化学学报, 2015, 73(11): 1196-1202.

Liu Yucan, Duan Jinming, Li Wei. Influence of Solution pH on Photolysis Intermediates and DegradationPathway of Diazinon during UV Irradiation Treatment[J]. Acta Chim. Sinica, 2015, 73(11): 1196-1202.

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