Simultaneous filtration and liquid chromatographic microextraction with subsequent GC-MS analysis to study adsorption equilibria of pesticides in soil,

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 (r