Multiresidue Determination and Uncertainty Analysis of Pesticides in Soil by Ultrafast Liquid Chromatography Coupled to Mass Spectrometry

Este trabalho apresenta os resultados da validacao de um metodo simples, rapido e de baixo custo de preparacao de amostras para a determinacao de residuos de pesticidas em solo por cromatografia liquida ultrarrapida acoplada a espectrometria de massas com ionizacao por electrospray. O metodo se baseia na extracao com acetonitrila assistida por ultrassom, centrifugacao e evaporacao, sem etapa de purificacao adicional. As recuperacoes foram avaliadas a partir de dois tipos de solo, apresentando resultados na faixa de 70-110%, com desvio padrao relativo menor que 20%. Os coeficientes de correlacao para as curvas analiticas de calibracao foram maiores do que 0,99. Os residuos de pesticidas foram detectados em solos no intervalo de 1-62 ng g -1 , dependendo do composto. A incerteza do metodo foi estimada a partir de diferentes experimentos de adicao e recuperacao e materiais certificados. O processo de extracao foi identificado como a principal fonte de incerteza e as incertezas expandidas para cada pesticida, utilizando-se um fator de cobertura de 2, situaram-se entre 8,4 e 33%. O metodo proposto foi aplicado para a determinacao de pesticidas em amostras reais. This work presents the validation results of a simple, fast and low-cost sample preparation method for the determination of pesticide residues in soil by ultrafast liquid chromatography coupled to electrospray ionization mass spectrometry. The method uses acetonitrile ultrasound-assisted extraction, centrifugation and evaporation step, without further cleanup. Recovery studies were performed for two soil blanks, presenting results in the range of 70-110% with relative standard deviation lower than 20%. The correlation coefficients for analytical calibration curves were higher than 0.99. Pesticide residues were detected in soils in the range of 1-62 ng g -1 , depending on the compound. The uncertainty of the method was estimated from different addition-recovery experiments and calculations from certificates. The extraction process was identified as the main source of uncertainty, and the expanded uncertainties for each pesticide, using a coverage factor of two, were between 8.4 and 33%. The proposed method was applied to the determination of pesticides in real samples.