Determinação de resíduos de agrotóxicos em água empregando microextração líquido-líquido dispersiva (DLLME) e cromatografia líquida de alta eficiência com detecção por arranjo de diodos (HPLC-DAD)

Abstract

Water is a natural resource of extreme importance, humans, animals and plants depends directly on it to survive. The state of RS stands out in national scenario as a big producer of many crops, which demand huge amounts of defensives of different chemical classes and toxicities. The intense use of these compounds was always associated to vantages and disadvantages to society. High productivity, better fruits conservation and pest control are clear benefits, however, the extensive use these substances has harm human health and the environment, like soil,water and air. Because of that, it is of extreme importance the study of analytical methods that are capable of monitor and quantify these compounds, stimulating scientific growth in water treatment and supporting more effective laws to control such substances. This work had as objective develop an analytical method for the determination of seven pesticides in surface water by dispersive liquid-liquid microextraction (DLLME) and determination by high-performance liquid chromatography with diode-array detection (HPLC-DAD). During the optimization of the DLLME method, different extractor and dispersant solvents, and different gradient programs were evaluated. The best results for the extraction were obtained using chloroform (150 μL) and acetonitrile (2 mL) as extractor and dispersant solvents, respectively. The mixture of both those solvents was rapidly added to the sample, which was then shaken and centrifuged, generating a sedimented drop containing the analytes extracted. The drop was withdrawn with a syringe, and the organic solvent was evaporated, then the analytes were redissolved in methanol, and sent to analysis in the HPLC system. The method validation, was performed through the linearity of the analytical curve, the limits of detection and qualification of the instrument and the method, the precision and accuracy were evaluated by the assays in the 10 and 50 mg L-1 concentration levels. Then, with the method validated, three water samples of different cities he state of form Rio Grande do Sul were analysed. The analytical curves were linear from 0,5 to 50 mg L with determination coefficient higher than 0,98. The recoveries were within the desired limits (50-120%), with relative standard deviation (RSD) lower than 20%. The validated method has as advantages the low organic solvent, and sample volume use, speed and high concentration factor. None of the samples showed contamination with the studied compounds.