Influência do método de extração, dos componentes da matriz e da temperatura da coluna na resposta cromatográfica para agrotóxicos

• Autor(a) principal: Santos, Lívia Carvalho
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2106
• topic: Efeito de matriz; Agrotóxicos; Cromatografia gasosa; Matrix effect; Pesticides; Gas chromatography; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

During the chromatographic analysis, components of the matrix contained in the extracts may influence the quantification of analytes, producing unreliable results. The change in the chromatographic response (due to the presence of co-extractives) receives the name of the matrix effect. The occurrence of matrix-induced effects and their extent are influenced by several factors such as analyte polarity, matrix analyzed type, chromatographic system historic (deposition of substances in the inserter), analyte concentration, etc. This study evaluated the influence of the matrix, the extraction method, the analyte concentration and the initial temperature of column chromatographic on the response (peak area) of eight pesticides (chlorothalonil, chlorpyrifos, thiamethoxam, procymidone, cyproconazole, iprodione, bifenthrin and azoxystrobin) at three concentration levels, using methyl parathion as internal standard. The extracts were obtained from the matrices red pepper, yellow pepper and tomato, by three extraction methods: solid-liquid extraction with purification at low temperature (SLE-PLT), solid-liquid extraction with salt induced partitioning (SLE-SIP) and matrix solid-phase dispersion (MSPD). The analyses were performed by Gas Chromatography with Electron Capture Detector (GC-ECD), with conditions that ensured a good analytes separation. The initial column temperature was evaluated at three levels: 60, 100 and 150 °C. The matrix effect was measured by the difference of the chromatographic response for each pesticide, analyzed in the organic extracts of three matrices obtained by three extraction methods, in relation the response in pure solvent, varying the initial temperature of the column. It was used the three level design with the data of each pesticide at a confidence level of 95% (α = 0,05), from the results. For most pesticides, the red matrixes contributed more significantly to the increase the matrix effect. The analytes responded differently in respect to temperature; in some cases the optimal temperature was 60 °C, in another 150 °C. Using the MSPD technique, the responses from the extracts approached those found in acetonitrile. It was also made a study of the stability of analytes in extracts prepared, which were stored and analyzed after 20, 40 and 60 days of the first analysis. The results of the responses were compared by paired t test at a confidence level of 99% (α = 0,01). The pesticide chlorothalonil and thiamethoxam were stable in all extracts until the 60th day of reading. Chlorpyrifos and procymidone had varied their concentration in the presence of co-extractives of red pepper, in 60th and 40th day of analysis, respectively. The cyproconazole had decreased their response in the presence of matrix components tomato from the 40th day of reading. Thus, it was possible to investigate the different variables influence on the chromatographic analysis and check the stability of pesticides during the monitoring period.