Relation of sorption behavior of agricultural chemicals in solid-phase extraction with their n-octanol/water partition coefficients evaluated by high-performance liquid chromatography (HPLC)

The HPLC method for the evaluation of the n-octanol/water partition coefficients (Pow) of agricultural chemicals was investigated, and the Pow values of 46 agricultural chemicals were determined by the proposed method. Then the sorption behavior of these chemicals in solidphase extraction(SPE) was investigated using eight different types of Sep Pak Plus cartridges and five eluents in the relation to these Pow values. The chemicals with a logPow below about 4.5 were completely retained onto the alkyl-modified silica and polystyrene cartridges, and easily eluted with any of the eluents except for n-hexane. The recovery of the chemicals with higher Pow values decreased with the increase of Pow values due to incomplete elution, but the extent of elution could be improved by adding methanol to the sample solution. Moreover, by back flush elution the chemicals with a logPow below about 5.5 could be completely recovered without the addition of methanol. However, in order for the complete elution of the extremely hydrophobic chemicals the addition of methanol was required even with the back flush. The results suggest that the Pow values evaluated with the HPLC method can be used as the most useful key parameter for the selection of the key conditions in SPE. It is interesting that the cyanopropylated-silica cartridge can retain the more hydrophobic chemicals so that it could be used for selective reversed-phase SPE for the extremely hydrophobic chemicals.