Described is a method for simultaneous determination of five herbicides (metribuzin, acetochlor, clomazone, oxyfluorfen and dimethenamid) belonging to different pesticide groups in soil samples. Developed headspace solid phase microextraction method (HS-SPME) in combination with liquid--solid sample preparation was optimized and applied for the analysis of agricultural samples. Optimization of microextraction conditions, such as temperature, extraction time and sodium chloride content was

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... med using 100 μm polydimethyl-siloxane (PDMS) fiber. The extraction efficiencies of methanol, methanol:acetone and methanol:acetone:hexane in 1:1 and 2:2:1 volume ratios, respectively, and the optimal number of extraction steps during the sample preparation, were tested as well. Gas chromatography-mass spectrometry was used for detection and quantification, obtaining relative standard deviation (RSD) below 13 %, and recovery values higher than 83 % for multiple analyses of soil samples fortified at 30 μg kg -1 of each herbicide. Limits of detection (LOD) were less than 1.2 μg kg -1 for all the studied herbicides.