Analysis and imaging of biocidal agrochemicals using ToF-SIMS

Abstract

ToF-SIMS has been increasingly widely used in recent years to look at biological matrices, in particular for biomedical research, although there is still a lot of development needed to maximise the value of this technique in the life sciences. The main issue for biological matrices is the complexity of the mass spectra and therefore the difficulty to specifically and precisely detect analytes in the biological sample. Here we evaluated the use of ToF-SIMS in the agrochemical field, which remains a largely unexplored area for this technique. We profiled a large number of biocidal active ingredients (herbicides, fungicides, and insecticides); we then selected fludioxonil, a halogenated fungicide, as a model compound for more detailed study, including the effect of co-occurring biomolecules on detection limits. There was a wide range of sensitivity of the ToF-SIMS for the different active ingredient compounds, but fludioxonil was readily detected in real-world samples (wheat seeds coated with a commercial formulation). Fludioxonil did not penetrate the seed to any great depth, but was largely restricted to a layer coating the seed surface. ToF-SIMS has clear potential as a tool for not only detecting biocides in biological samples, but also mapping their distribution.

In situ chemically specific mapping of agrochemical seed coatings using stimulated Raman scattering microscopy

“…A major drawback when performing forward‐detected SRS microscopy is the need for sample sectioning prior to imaging since it could perturb the distribution of the seed coating. Although the use of cryo‐sectioning would allow us to further immobilize the coating material than hand sectioning, the seed sectioning is still a destructive and time‐consuming process . We therefore performed imaging in the epi‐detected SRS images with the introduction of quarter‐wave plate and polarizing beam splitter in the epi‐direction, as illustrated in Figure A.…”