A new method for the extraction of pesticide residues from soil was developed, optimized, validated and applied to real samples. The technique consisted of combining single-drop microextraction and solid-liquid extraction with low temperature partitioning (SLE/LTP-SDME) followed by analysis using gas chromatography with electron capture detection (GC/ECD). This method was used to determine the presence of alachlor, methyl parathion, trifluralin, endrin, lindane, dieldrin and dichloro-diphenyl-trichloroethane (4,4’-DDT) in soil samples. Recoveries ranging from 67.2 to 122.5% were achieved, coefficients of variation (repeatability) were lower than 22.4% and limits of detection ranged from 0.18 to 0.59 µg kg-1. Recovery from soils fortified with different concentrations of the pesticides ranged from 61.5 to 123.5%. The new method combines the primary advantages of the two techniques: purification of the sample using SLE/LTP and preconcentration using SDME. The new method also enables the determination of low volatility compounds without requiring the sample to be heated.

O monitoramento de pesticidas em amostras ambientais em baixas concentrações é necessário devido aos riscos que estes compostos representam a saúde humana e ao meio ambiente. Neste trabalho, o método microextração em gota única (SDME) foi otimizado e validado para a determinação das concentrações traço de oito pesticidas em água utilizando cromatografia gasosa com detector por captura de elétrons (GC/ECD). A cinética de transferência de matéria da fase aquosa para a fase orgânica durante o processo de extração também foi avaliada. O método mostrou recuperações entre 89,5 e 122,7%, com coeficientes de variação menores que 22,9%, e os limites de detecção entre 5,9 e 58,9 ng L-1. O método foi aplicado a amostras fortificadas em diferentes níveis de concentração, e recuperações entre 50,5 e 148% foram obtidas. O processo de extração pode ser descrito pelo modelo de difusão de Noyes-Whitney, e a parationa metílica apresentou a maior taxa de transferência entre as duas fases.

The monitoring of pesticides in environmental samples at low concentrations is needed due to the risks that these compounds can pose to human health and the environment. In this work, a single drop microextraction (SDME) method was optimized and validated for the determination of trace concentrations of eight pesticides in water, using gas chromatography with electron capture detector (GC/ECD). The kinetics of the transfer of material from the aqueous phase to the organic phase during the extraction process was also evaluated. The method showed recoveries between 89.5 and 122.7%, with coefficients of variation smaller than 22.9%, and detection limits between 5.9 and 58.9 ng L-1. The method was applied to spiked samples at different concentration levels, and recoveries between 50.5 and 148% were obtained. The extraction process could be described by the Noyes-Whitney diffusion model, and methyl parathion showed the highest rate of transfer between the two phases.