Determinação de resíduos de pesticidas em plantas de arroz empregando QuEChERS modificado e GC-ECD

Abstract

Rice culture is an activity that has currently been gaining more importance due to its use in human feeding, allowing enough food and acceptable quality to the population. There is a great concern regarding the intensive use of pesticides, the main strategy employed in the countryside to combat and prevent plagues, as well as the residues resulting from such practice. This paper has been developed and validated on an analytical procedure, using the QuEChERS modified extraction approach and gas chromatography with electron-capture detection (GC-ECD) for the determination of residual insecticides lambda-cyhalothrin and bifenthrin and azoxystrobin fungicides and trifloxystrobin in rice plants. The QuEChERS modified method was applied in an initial stage of extraction using 3.0 g of rice plants in which was added 15 mL of acetonitrile containing 1% (v/v) acetic acid, followed by a partition step after the addition of a mixture of anhydrous salts (3 g of magnesium sulphate and 1.7 grams of sodium acetate). Next, the clean-up stage was carried out 4 mL extract using 200 mg of activated charcoal and 600 mg of magnesium sulfate and the analysed by GC-ECD using an apolar DB-5 column. During method validation, LOD; LOQ; linearity; precision (repeatability and intermediate precision); and accuracy, evaluated in terms of recovery, were determined. Using this method, LOQ quantities were 1 mg kg-1 for azoxystrobin and 0.05 mg kg-1 for lambdacyhalothrin, bifenthrin and trifloxystrobin. The analytical curves presented linearity between 0.01 and 1.0 mg L-1, with coefficient of determination greater than 0.993. The method had shown good precision, with RSD values smaller than 19.0%, and accuracy, with recoveries between 71.2 and 103.6%. The method was considered adequate to the analysis of pesticides in rice plants, considering that all validation parameters meet the levels required for validation of chromatographic methods. After being validated, the method was applied to the study of the residual concentration of pesticides in rice plants, from rice crops irrigated with an experiment carried through at the UFSM Campus; where the pesticides azoxystrobin, bifenthrin, lambda-cyhalothrin, and trifloxystrobin were individually applied in 2007/2008 harvest. All pesticides in this study were detected up to approximately twenty (20) days after being applied.