RESUMEN
Two simple and straightforward sample preparation methods were developed for the multiresidue analysis of post-emergence herbicides in loam soil that are commonly used in rice crop cultivation. A number of strategic soil extraction and cleanup methods were evaluated. The instrumental analysis was performed by HPLC with a diode array detector. The best compromise between the recoveries (69-98%) and good repeatability (RSD < 15%) was obtained using either methanol or methanol-ethyl acetate (70 + 30, v/v) as extraction solvents without any further cleanup. For the first time, residues of metsulfuron methyl, bensulfuron ethyl, bentazone, cyhalofop butyl, pyrazosulfuron ethyl, propanil, and clomazone were analyzed simultaneously. Quinclorac and bispyribac sodium were also assayed, but their recoveries were below 50%. Both methods had an LOD of 0.7 microg/kg and could accurately determine the residues at the 2 microg/kg level. These two methods could not be applied directly to other soil types as the recoveries strongly depended on the soil composition. The developed methodologies were successfully applied in monitoring 87 real-world soil samples, in which only propanil (6 to 12 microg/kg) and clomazone (15 to 20 microg/kg) residues could be detected.
