DISEÑO DE EXPERIMENTOS APLICADO EN LA OPTIMIZACIÓN DEL MÉTODO DE EXTRACCIÓN QuEChERS PARA LA DETERMINACIÓN DE PLAGUICIDAS ORGANOCLORADOS Y ORGANOFOSFORADOS EN SUELOS

Abstract

The QuEChERS methodology was implemented for the extraction of fourteen pesticides, ten organochlorines and four organophosphates in soil samples. The analysis was carried out by gas chromatography coupled to a quadrupole ion trap in tandem mode (MS 2 ). The extraction of the pesticides by the selected methodology is affected by different factors. Therefore, the extraction process optimization included the use of two experimental designs: a Taguchi orthogonal design to determine most influential factors and, subsequently, a fractional factorial design 2 5-1 to determine the optimal preparative conditions. Results showed that the pH, sonication and the use of cleaning adsorbents are irrelevant factors in the preparatory process. By contrast, the amount of water in the matrix, the relationship sample:solvent, and the amounts of MgSO 4 and NaCl as partition salts, play an important role in the process. The final method consisted in the soil hydration with 5 mL of water type I, using 10 g of sample, stirring for 1 min, addition of 10 mL of acetonitrile as extractor solvent, salting out with 2 g of MgSO 4 , 2 g NaCl, and final cleansing of the extract with 100 mg of octadecylsilane (C 18 ), 10 mg of graphitized carbon and 600 mg of MgSO 4 (per mL of extract). With the final method, the pesticides studied can be extracted quantitatively from the matrix, with recoveries between 70-120 %, coefficients of variation less than 10 % and detection limits between 4.9-21.7 μg/kg.