Desenvolvimento de método analítico de extração sólido-líquido com partição à baixa temperatura de resíduos de tiametoxam em solo destinado ao plantio de feijão

Abstract

The destination of pesticides, regardless of the type of application, is commonly the environmental compartments, such as the soil. In this compartment, the pesticide molecule can follow different paths, affecting several ecosystems and living beings. Thiamethoxam is one of the most applied insecticides in Brazilian grain monocultures. However, methods to monitor its residues in the soil are still incipient. This study sought to develop an analytical methodology to determine thiamethoxam residues in red latosol used in bean planting. The method chosen for soil sample preparation was solid-liquid extraction with a low-temperature partition (ESL-LTP) and quantification of extracts by high-performance liquid chromatography with photodiode array detection (HPLC-DAD). The ESL-LTP method was optimized under the main factors that affect the extraction of thiamethoxam from soil samples, such as type of extractor solvent, amount of sample, volumes of water and extractor solvent, the addition of salt, and freezing time. In this step, optimal conditions for the ESL-PBT of thiamethoxam in soil were defined as acetonitrile as extractor solvent, using 4 mL for 2 mL of 10 % (w/v) KCl aqueous solution for 1.0 g of the soil sample, with about 86 % recovery of thiamethoxam. After the optimization, the method validation was performed, regarding the selectivity, linearity, working range, quantification limit, accuracy, precision, and robustness parameters, following the guidelines for the analytical method validation of the European Community. The method for the determination of thiamethoxam in soil samples presented recovery rates in the range of 70 to 98 %; good precision, with relative standard deviations < 6 %; limit of quantification of 0.04 mg kg-1 of thiamethoxam in soil, lower than the maximum residue limit in bean grains of 0.3 mg kg-1. Thus, the proposed analytical methodology proved to be quick, simple, and efficient for the extraction and quantification of thiamethoxam in red latosol samples, typical of the Brazilian Cerrado region. The method can be applied in soil samples of bean cultivation, with potential contamination by the insecticide.