Continuous Liquid-Liquid Extraction of Organic Pesticides from Aqueous Solutions

Abstract

Liquid-liquid extraction (LLE) is considered by most residue analysts to be the best method for quantitative recovery of organic pesticides from aqueous solutions. Continuous liquid-liquid extraction is a logical extension of the process. This paper reviews the LLE process especially the alternative of continuous LLE for the isolation of organic pesticides from aqueous solutions. Trends and user problems are noted. A continuous liquid-liquid extraction apparatus with capabilities for continuous solvent recycling and sample enrichment is described. The principal parts of this design are a helix Teflon coil mixing chamber, a column phase-separator, and an evaporative concentrator. Initial experiments were made to evaluate the design. Extraction efficiencies ranging from 85 to 93 percent were obtained for five organophosphate pesticides extracted from water with benzene under the optimized conditions of coil length, helix diameter, flow rate, and water to solvent ratio. The apparatus is simple and economic to build. It is contamination-free as all parts in contact with water and solvent are made either of Teflon or glass. Complete automation of this apparatus is possible by adding liquid-level controllers, solenoid valves, and electronic relay systems.