Desenvolvimento de método de determinação de resíduo de tiametoxam em águas de lixiviação do feijoeiro, empregando extração líquido-líquido com partição à baixa temperatura

Abstract

The success of crops and the quality of food produced depend on natural factors, such as climate and soil, and the strategic use of chemicals to combat pests. In bean crops, thiamethoxam is the main chemical that controls pests, such as aphids and whiteflies. This insecticide belongs to the neonicotinoid class, and because it is highly soluble in water and has low retention in soils, it can be leached and transported to groundwater. Due to the possibility of contamination of these waters, this study developed a method to determine thiamethoxam residues in leached water samples by high-performance liquid chromatography with diode array detection (HPLC-DAD). For this purpose, liquid-liquid extraction with low-temperature partitioning (LLE-LTP) was used because it is a simple technique with low interference from the analyst and is efficient in extracting pesticides in complex matrices. Thus, initially, a univariate optimization of the factors comprising the ELL-LTP, such as selectivity of the extracting solvent, solvent, sample volume, and freezing time, was carried out. In this stage, acetonitrile was identified as the best extractor solvent, using a ratio of 2.0 mL of acetonitrile to 2.0 mL of leached water sample and a two-hour freezing time. Under these conditions, the thiamethoxam recovery of 110 ± 1 % was obtained, evidencing the influence of organic components co-extracted from the soil during leaching. The method was then validated for its selectivity, limit of quantification (LOQ), linearity, precision, accuracy, and robustness according to the criteria established by the analytical method validation guide proposed by the European Community (SANTE/11312/2021.V2). Through this guide, it was possible to prove that the proposed method is selective, accurate, and precise, resulting in an average recovery of 103 ± 10 %. The recorded LOQ was 10.0 µg L-1 of thiamethoxam in water, lower than the maximum permitted limit of thiamethoxam residues in water of 36 µg L-1 . The recorded matrix effect was 20.3 %, and the robustness of several method conditions was demonstrated. In the simulation of bean cultivation, thiamethoxam was applied in spraying, seed treatment, and as bioactive fertilizers. The insecticide was detected in water samples collected 15 and 30 days after spraying, indicating the efficiency of the LLE-LTP-HPLC-DAD method for determining thiamethoxam residues in water leached from bean crops.