Determination of fenthion and fenthion-sulfoxide, in olive oil and in river water, by square-wave adsorptive-stripping voltammetry

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO₄. The metabolite gives rise to a peak due to an adsorptive-reductive process at −0.786 V. Fenthion is isolated from olive oil by carrying out a solid–liquid extraction procedure using silica cartridge, followed by a liquid–liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g⁻¹ and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid–liquid partitioning with trichloromethane. The detection limits are 0.41 ng g⁻¹ and 0.44 ng g⁻¹, for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.