Rationale of the solvent selection for soil extraction of pesticide residues

Abstract

No obvious consideration for the solubility of the residual pesticide in the organic solvent used was reported in the literature. The primary criteria for choosing solvent have been utilitarian ones such as the absolute extraction efficiency, minimal amount of co-extractives and subsequent interference, minimal cleanup steps of the extract, and reproducibility of residue recovery. An analysis of the solvent choice in reported single-solvent methods of analysis of pesticide residues in soil was made from a review of the literature from 1960 to 1981. Tests of associations between molecular and chemical properties of the pesticide and the extractant properties were conducted. A data base of 82 compounds and their associated exractants showed a wide range of lipophilicity and a three-cluster pattern. In general, researchers tend to employ more polar solvents in the extraction of more nonpolar pesticides. Methanol and acetone were the most frequently used solvents. In 51 methods, an overall positive correlation exists between the lipophilic character of the pesticides (K(ow) or parachor) and their solubility in the organic extractant. Three binary relationships showed that there is a corresponding increase in solubility with an increase in K(ow) within the range 2.14 to 5.89. The rate of change of log K(ow) as a function of log S was 0.2 for compounds in the log K(ow) range of 2.14 to 3.69, and it was 0.4 for compounds in the 4.1 to 5.9 range. The predictability of suitable solvents for the soil extraction of a chemical is a plausible process when molecular properties and solvent properties are properly matched.