Detecção Eletroanalítica e Estudo do Mecanismo de Oxidação do Pesticida Dimetomorfe

Abstract

Dimethomorph (DIM) belongs to the class of morpholinic fungicides, it has systemic action, it is persistent in food matrices and in planting soils where was applied and a possible endocrine interferent, justifying the development of methodologies for detection and quantification of this compound. In the electrochemical study can be seen that the DIM had electrochemical process diffusion-controlled and characterized as quasi-reversible, with electrode potential of approximately 1.28 V vs. Ag/AgCl/Cl-(KCl sat.) electrode and involving two electrons transfer. In the development of electroanalytical methods using the square-wave voltammetry and the boron-doped diamond electrode, it was found that the best experimental and voltammetric conditions were obtained in Britton-Robinson buffer pH 3, as supporting electrolyte, pulse potential frequency of 30 s-1, square-wave amplitude of 50 mV and potential step increment of 2 mV. From these conditions it was possible to develop an analytical method with a linear range from 4.57x10-6 to 3.78x10-4 mol L-1, detection limit of 3.11x10-7 mol L-1, quantification limit of 1.04x10-6 mol L-1, 0.13% of repeatability (n = 10) and 0.92% of reproducibility (n = 5). The evaluation of the interference of the ionic compounds present in the supporting electrolyte and the Mancozebe (MZB), present in DIM co-formulations, in the accuracy and precision of the methodology showed that these species have little influence. The recovery in electrolyte was of 97.25 ± 0.70%, with 95% confidence, and BIAS of 2.74%. The percentage of MZB interference, in different concentrations, was less than |10%|. The application of the proposed methodology for determining of the DIM in fresh grapes and red wine showed a percent recovery equal to 101.0 ± 12.1% and 105.1 ± 10.8% with 95% confidence, respectively, and BIAS less than 6 %. Based on the quantum-chemicals information, we can infer that the site of oxidation of DIM is the non-aromatic double bond. The data obtained by gas chromatography-mass spectrometry led to the conclusion that the electrodic substrate nature does not interfere in the overall mechanism of the DIM electrooxidation reaction, in which is formed the (4-chlorophenyl)-(3,4-dimethoxyphenyl)methanone as major product.