Understanding the sorption equilibria of microcontaminants in soils requires the determination of the adsorbed analytes as well as those remaining in solution. On-line filtration-plus-LC-type microextraction offers an efficient alternative to the time-consuming classical procedures. The feasibility of a new simultaneous filtration-plus-liquid-chromatographic microextraction system with subsequent GCMS to study the partition equilibrium of pesticides in the interface soil-water was investigated. The method allows the determination of the amount of pesticide adsorbed in the soil and that remaining in solution by a single injection of the total slurry. As an example, the adsorption equilibria of selected pesticides, ranging from relatively polar triazines to nonpolar compounds such as hexachlorobenzene or bromophos-ethyl, in an organic soil were studied. Once separated and preconcentrated, the filter and the solid-phase cartridge fractions were independently dried by a stream of nitrogen, extracted with methyl acetate, and analyzed by GC-MS. The standard deviations for the total procedure were lower than 6.2% (soil) and 10% (solution). The soil-water partition coefficients calculated for the selected compounds showed a good correlation with published octanol-water partition coefficients (r2 = 0.973). This demonstrates clearly the practicality of the proposed methodology for adsorption equilibrium studies. | Understanding the sorption equilibria of microcontaminants in soils requires the determination of the adsorbed analytes as well as those remaining in solution. On-line filtration-plus-LC-type microextraction offers an efficient alternative to the time-consuming classical procedures. The feasibility of a new simultaneous filtration-plus-liquid-chromatographic microextraction system with subsequent GC-MS to study the partition equilibrium of pesticides in the interface soil-water was investigated. The method allows the determination of the amount of pesticide adsorbed in the soil and that remaining in solution by a single injection of the total slurry. As an example, the adsorption equilibria of selected pesticides, ranging from relatively polar triazines to nonpolar compounds such as hexachlorobenzene or bromophos-ethyl, in an organic soil were studied. Once separated and preconcentrated, the filter and the solid-phase cartridge fractions were independently dried by a stream of nitrogen, extracted with methyl acetate, and analyzed by GC-MS. The standard deviations for the total procedure were lower than 6.2% (soil) and 10% (solution). The soil-water partition coefficients calculated for the selected compounds showed a good correlation with published octanol-water partition coefficients (r2 = 0.973). This demonstrates clearly the practicality of the proposed methodology for adsorption equilibrium studies.

L. Ramos thanks the Spanish Ministerio de Educacion y Cultura for financial support.

Peer Reviewed