Microwave-assisted solvent extraction of the herbicide methabenzthiazuron from soils and some soil natural organic and inorganic constituents. Influence of environmental factors on its extractability

Abstract

A microwave-assisted solvent extraction (MASE) method for the determination of methabenzthiazuron (MBT) in soil samples by HPLC-DAD (diode array detection) was evaluated. Spiked soil samples having different physico-chemical properties, and selected soil-derived matrices with diverse MBT adsorption capacity, characterized by their Freundlich equation K_f values, were used to verify the method applicability to a broad range of different soils. The spiking procedure was considered a crucial point to reproduce as closely as possible the solute–soil adsorption taking place in the natural environment. Ageing effects, where the compound could diffuse into inaccessible locations within the soil matrix in view of its great stability, were considered of particular concern. In spite of the heterogeneous physico-chemical properties of soils under study, recoveries were greater than 90%. Performance of the MASE procedure correlated highly with the adsorption capacity of soil-derived matrices: the lowest recoveries were for illite (67–73%), among the mineral surfaces, and for a humic acid (67–72%), among the organic fractions. Intra-assay variation for each type of sample soil range from 0.40 to 3.89% (RSD). Limits of detection and quantification were 0.047 and 0.15 µg g⁻¹, respectively. Analyte residence time was not a very significant factor on the extractability.