Background: Agrichemicals are widely used to to protect crops from pests and enhance crop yields, but represent an important class of potential environmental contaminants. . Photochemical degradation is one of the primary pathways by which agrichemicals can break down in nature . However, our current knowledge of agrichemical photolysis breakdown products is unreliable, particularly in relation to identifying toxic end products .
Objectives: To obtain a better understanding of the identity of agrichemical photoproducts, the following goals are necessary:
• Develop a new methodology for simplifying the identification of the direct photolysis products of an agrichemical. The method should at least be able to provide structural identification equivalent to that currently obtainable by MS, but more definitive structural identification (e.g. spectroscopic) of photoproducts is highly desirable.
• Develop a new methodology for performing “on-line” analysis of a photolysed agrichemical in solution, to allow for continuous sampling so that time-dependent changes in the solution composition can be followed, as well as identification of short-lived intermediates. Again, structural identification equivalent to that obtainable by MS is essential, with more definitive structural spectroscopic identification being highly desirable.
Experimental Approach and Novelty: We propose to meet these objectives by:
1. Photolysing key agrichemicals in the gas-phase using laser-interfaced mass spectrometry
Within solution, photolysis pathways are affected by many variables , so we propose to dramatically reduce this complexity by taking the agrichemical out of solution and studying its breakdown pathways in the gas-phase for the first time. These experiments will use the Dessent group’s novel laser-interfaced mass spectrometer (LIMS), which allows the gas-phase UV-VIS absorption spectrum to be recorded, along with MS identification of primary and secondary photoproducts [5, 6]. A range of key agrichemicals will be studied.
2. Developing full “on-line” analysis of photolysis of agrichemicals in solution
In the next stage, we will develop on-line solution photolysis detection, linked to the LIMS instrument. This will allow us to use MS to characterise any photoproducts/reaction intermediates, and also perform UV/VIS spectroscopy on them within the LIMS machine, providing definitive structural identification. This would be the first such experiment developed internationally.
3. Comparative assessment of the results and application to real world samples
In stage 3, we will compare the results obtained in Steps 1 and 2 against off-line photolysis (manual sampling of photolysed solutions). It will also be important to perform additional analysis of photolysed solutions using HPLC-MS/MS (in collaboration with JETO) .
Training: Full training in MS and (soft ionization techniques and HPLC) and laser photochemistry (use of class 4 laser systems and diode lasers) will be provided, along with training in data analysis and storage. The student will be strongly encouraged to participate in national and international conferences, allowing them to develop oral and presentation skills.
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