Pressurized Fluid Extraction of Nonpolar Pesticides and Polar Herbicides Using in Situ Derivatization

摘要

Analysis of polar acidic herbicides has traditionally pre-sented a challenge because of their strong adsorption to and ionic interactions with soil. One approach which has been successful for extraction of these polar compounds from soil is supercritical fluid extraction (SFE) coupled with in situ derivatization. This technique involves the addition of common derivatization reagents duecdy into the extraction chamber, where the acid herbicides e derivitized to extractable esters or ethers. l~ andy describes the application of an in situtechnique to pressurized fluid extraction (PVE) fur the herbicides 2,4-D, 2,4,5-T, dicamba, silvex, Irichlopyr, and bentazone. The efficiency of in situ derivatiration PFE for these analytes is compared with a conventional basic extraction method followed by ex situ derivatization. The variables of temperature, pressure, static extraction time, and derivatization-reagent amount were optimized for recovery of these analytes from soil. Average recovery for these six analytes was 107% for in situ derivatization PFE from spiked sand, 93% for the same method from a high-concentration spiked soil (50 mg/kg), and 68% for the optimized in situ derivatization PFE method from low-concentration soil (0.5 mg/kg). The in situ derivatization PFE method has substantial advantages of simplicity of methodology and reduction in extraction time compared with the conventional technique. A second in situ deriva-tization PFE strategy was investigated using sodium EDTA in the extraction chamber for the extraction of 2,4-D from soil. Preliminary results demonstrate improved recovery with the use of Na4EDTA. Extraction efficiency of PFE for nonpolar organochlorine insecticides and slightly polar triazine herbicides from soil is also presented and com-pared with that of Soxhlet extraction.