Coprecipitation-assisted coacervative extraction coupled to high-performance liquid chromatography: An approach for determining organophosphorus pesticides in water samples

Abstract

An analytical methodology based on coprecipitation assisted coacervative extraction cop-CAE) coupled to High Performance Liquid Chromatography and UV-visible detection was developed for analysis of five organophosphorus pesticides (OPPs), including fenitrothion, guthion, parathion, methidathion and chlorpyrifos, in water samples. It is the first time that cop-CAE was used for extraction and preconcentration of OPPs from water for further determination by HPLC. The effects of relevant physic-chemical variables on the analytical response of each OPP (pH, precipitant concentration, surfactant concentration, stirring time, equilibration time and temperature) were studied and optimized, as well as the working conditions for coupling cop-CAE to HPLC-UV. Under optimized conditions, the resulting methodology was as follows: an aliquot of 10 mL of water sample was placed into a 15 mL centrifuge tube where 0.5 mL of sodium citrate 0.1 M, pH 4, 0.08 mL of aluminum sulfate 0.1 mM and 0.7 mL of SDS 0.1 mM were added and homogenized for 8 min using a vortex stirrer to induce the formation of the admicelles. The resulting cloudy solution was kept at 25 °C for 5 min for equilibration. After centrifugation the coacervate rich-phase and supernatant were separated. The resulting supernatant was removed and discarded. A 0.7 mL aliquot of the coacervate rich-phase was transferred to 2 mL vial and dissolved with 300 µL of methanol. An aliquot of 20 µL of the resulting homogeneous solution was injected into the HPLC-UV for analysis. The method detection limits for fenitrothion, parathion, guthion, methidathion and chlorpyrifos under optimized conditions was 83, 35, 35, 57 and 12 ng L-1, respectively. The RSD (%) for the studied analytes were < 3% (n=3). Recovery values ranged from 78 to 93%. The proposed analytical methodology was successfully applied for the analysis of five OPPs in different water sample of Mendoza city.