Etude des mécanismes d'ablation-ionisation laser de pesticides adsorbés sur membranes par spectrométrie de masse à transformée de Fourier

Abstract : Laser desorption/ionisation coupled with Fourier transform mass spectrometry is an ever growing technique with promising applications in the field of surface analysis. However, this method is very sensitive to the experimental parameters. Through this work, after having defined the physical phenomena invoked in the process, we have put the stress on the practical implications of the microscopic processes which have to be taken into account during the analysis. Several examples illustrate this demonstration. The feasability of the method for the analysis of pesticides adsorbed on solid phase extraction membranes has been evaluated for the first time. Five compounds with very different structures and various applications in agriculture have been analysed by classical mass spectrometry and their fragmentation products have been compared to those obtained by laser desorption at 248 nm wavelength. The analysis of the membrane by laser desorption has allowed us to evaluate the possible interferences and the ablation depth at various irradiances. The experiments concerning atrazine and its metabolite have allowed us to propose two distinct ionisation mecanisms : gas phase ionisation versus "true" desorption. Moreover, at the 248 nm wevelength, the various compounds adsorbed on membranes have shown very different behaviors which are better explained by their respective octanol/water partition coefficient than by their absorbance at the laser wavelength. The use of a tripled Nd-YAG laser has allowed the detection of the compounds which couldn't be detected at 248 nm and to confirm the hypothesis of a deeper adsorption of these compounds into the membrane
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Christophe Masselon. Etude des mécanismes d'ablation-ionisation laser de pesticides adsorbés sur membranes par spectrométrie de masse à transformée de Fourier. Autre. Université Paul Verlaine - Metz, 1997. Français. ⟨NNT : 1997METZ012S⟩. ⟨tel-01777199⟩

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