Determination of multi-class herbicides in soil by liquid-solid extraction coupled with headspace solid phase microextraction method

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 performed using 100 mu m 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 mu g kg(-1) of each herbicide. Limits of detection (LOD) were less than 1.2 mu g kg(-1) for all the studied herbicides.