Influência do pH, dos constituintes da matriz e do estádio de maturação do tomate na análise de agrotóxicos por cromatografia gasosa

• Ano de defesa: 2012
• Autor(a) principal: Sousa, Flaviane Aparecida de
• Orientador(a): Neves, Antônio Augusto
• Banca de defesa: Coutrim, Maurício Xavier , Queiroz, José Humberto de , Oliveira, André Fernando de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Agroquímica
• Departamento: Agroquímica analítica; Agroquímica inorgânica e Físico-química; Agroquímica orgânica
• País: BR
• Palavras-chave em Português: Efeito de matriz; Cromatografia gasosa; Agrotóxicos
• Palavras-chave em Inglês: Matrix effect; gas chromatography; pesticides
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA
• Link de acesso: http://locus.ufv.br/handle/123456789/224

The present study aimed to deepen the studies related to matrix effect on chromatographic analysis of pesticides. Initially we sought to evaluate the difference in chromatographic response of eleven analytes (chlorothalonil, chlorpyrifos, methyl parathion, procymidone, endosulfan, iprodione, permethrin, λ-cyhalothrin, cypermethrin, deltamethrin and azoxystrobin) when prepared in pure solvent and in organic extracts obtained by solid-liquid extraction with partition at low temperature (SLE-PLT) or liquid-liquid extraction with partition at low temperature (LLE-PLT) of seven matrices (tomato, pineapple, grapes, water, potato, apple and soil). The Principal Component Analysis (PCA) was used to evaluate the results obtained and resulted in the grouping of matrices: pineapple, tomato and grape (a group), potato, apple and soil (another group). The matrices tomato, pineapple and grape caused matrix effects positive in most pesticides and matrices potato, apple and soil caused a decrease in the response of pesticides. Analyzing the results showed a common characteristic of matrices that were grouped by PCA: pH values of the matrices tomato, grape and pineapple are around 4.0. The matrices potato, apple and soil have higher pH, around 6.0. Distilled water samples had their pH values adjusted with glacial acetic acid solution to values identical to matrices most acidic: grape, pineapple and tomato. It was noted that acidification of the water was a decrease in the chromatographic response of the pesticides similar to those results found for samples of pure water. The results demonstrating that the pH of the samples does not influence the properties of the pesticide in the organic phase, and thus the pH is not the factor directly responsible for the largest matrix effect observed for samples more acidic. However it was observed that organic extracts the matrices more acidic when obtained with alkaline solution of Na2HPO4 (pH around 7.0) had less intense staining, indicating that pH was related to the extraction of co-extractives into the organic phase. In a next step we evaluated the influence of pH on the chromatographic response of nine pesticides (chlorothalonil, chlorpyrifos, methyl parathion, procymidone, endosulfan, iprodione, permethrin, deltamethrin and λ-cyhalothrin). At this stage we used three matrices (potato, apple and soil), which had pH values of the extraction mixture changed to investigate differences in the chromatographic response of pesticides. Aqueous extracts were obtained by of the matrices ESL-PBT using a specified volume of distilled water (pH around 6.0) and using the same volume of water with the pH changed to 3.6 with addition of glacial acetic acid. It was observed that when the pH of the water was changed to 3.6 more coextrativos were extracted into the organic phase, therefore most effect on chromatographic response of the analytes was observed. The Principal Component Analysis showed the formation of two distinct groups: one formed by matrices containing water at pH = 6.0 and other matrices with water at pH = 3.6. Ultimately, the influence of maturation stage of tomato, which was a matrix that caused significant effect on the response of pesticides, has been evaluated. At this stage, five insecticides belonging to different groups separated by PCA in the previous stages of the work were selected for study (permethrin, iprodione, chlorothalonil, chlorpyrifos and deltamethrin). The results showed that as the fruit matures, a larger amount to co-extractives is found. The co-extractives lycopene and β-carotene influence directly in the chromatographic response of the analytes. When examining the influence of such components of tomato together with other matrices, it was observed that these are responsible for the largest matrix effect in the analysis of pesticide mainly for the pesticide deltamethrin.