Desenvolvimento e validação de método para determinação de agrotóxicos em água por microextração líquido-líquido dispersiva

Abstract

This work aimed to develop and validate a method for the determination of the pesticides trifluralin, metribuzin, malathion, metolachlor, α-endosulfan, β-endosulfan, endosulfan sulfate, λ-cyhalothrin and permethrin in water using dispersive liquid-liquid microextraction (DLLME).n-Hexane, chloroform and toluene-hexane mixture (60:40 v /v) were used as solvent extractor. The selection of extraction solutions was based on literature data and on the solubility parameters of Hildebrand / Hansen. The extraction procedure consisted on powering 7,5 mL of water samples spiked with the pesticides in a 15 mL test tube 750 μL of acetone as dispersing solvent and by 150 μL of extracting solvent. After that, the test tube was agitated by vortex for 10 seconds and centrifuged at 4000 rpm for 5 minutes. Then, 100 μL of the supernatant organic phase was transferred to an insert of 300 μL and automatically injected into a gas chromatograph coupled to a mass spectrometer. Among the solvents evaluated hexane: toluene (60:40, v/v) mixture showed an extracting capacity comparable to chloroform and therefore was selected for the remaining tests. Among the variables evaluated only stirring and addition of disperser solvent exerted a positive significant effect (t 95%) on the extraction procedure, while the addition of salt had a significant negative effect (t 95%). It was verified that there was no matrix effect in the extraction procedure. The DLLME provided recovery percentages of 47-115% with a RSD of up to 16%. The detection limits ranged between 0.1664 and 0.0063 μg L-1 whereas method quantitation limit was 2,0 μg L-1 for all analytes studied. Once validated, the method was applied to field samples collected in a river situated at an important agricultural region of Mato Grosso. In these samples were detected only the isomers of permethrin were detected. The results suggest that the proposed method can be an alternative for the determination of analytes in water, with the advantage of being fast and use a very small amount of solvent.