Otimização e validação de métodos de extração para determinação do herbicida florpirauxifen-benzil em solo e arroz.

Abstract

Florpyrauxifen-benzyl is a herbicide belonging to the synthetic auxin class that was released in Brazil in 2019, for rice, sugar cane, corn and soybean crops. By virtue its recent release, there are still few validation studies on waste extraction methodologies and analysis to date. Given this scenario, it is important to study new extraction and analysis methodologies that can be applied to quantify waste. Therefore, this study aimed to optimize and validate solid-liquid extraction with low temperature purification (SLE-LTP), for the determination of florpyrauxifen-benzyl, in soil and rice matrices, using high-performance liquid chromatography coupled to detection by diode array (HPLC-DAD). The extraction method used 4.0 g of matrix, 4 mL of water and 8 mL of extractor phase. The system was homogenized and frozen at – 20 °C for one hour. Then, part of the extract was recovered, evaporated, resuspended in solvent and stored in a freezer until analysis by HPLC-DAD. To development of the methodology for the rice matrix, a clean-up stage needed to be added, due to the yellowish and greasy appearance of the extract, which was recovered after the drying stage. They were optimized chromatographic conditions and compound extraction conditions for the studied matrices. The best chromatographic conditions for the soil matrix were achieved using a Poroshell column, temperature of 30 °C, mobile phase composition of acetonitrile and water (85:15 v/v) with 0.1% (v/v) formic acid, 243 nm as wavelength and flow of 0.3 mL min-1. During SLE-LTP, six extractor phases were evaluated. The best extracting phase was acetonitrile, containing 0.1% (v/v) formic acid, which presented a recovery rate of 104.0% and relative standard deviation (RSD) of less than 4.0%. They were obtained a detection limit of 5 µg kg-1 and a quantification limit of 20 µg kg-1. The stability study presented a result of 17.5 days for the half-life time of the compound. The best chromatographic conditions for the rice matrix were achieved using Kinetex column, temperature of 25 °C, mobile phase composition of methanol and water (78:22 v/v), 260 nm as wavelength and flow of 0.3 mL min-1. The optimal extraction condition was obtained using acetonitrile and water (2:1) as the extraction phase, followed by clean-up of the extracts with alumina in the proportion of 50 mg of alumina per mL of extract. The recovery percentages achieved were close to 100%, with a relative standard deviation (RSD) of less than 9.0%. The result presented a significant matrix effect (184.3%), but the methodology was precise, accurate, linear and selective, with a quantification limit of 5.0 μg kg-1.