Quantification of Phenylurea Pesticides by HPLC/ECD and Photolysis

Abstract

Phenylurea pesticides were quantified in the picomole range using electrochemical detection after reversed-phase liquid chromatographic separation. Hydrodynamic voltammograms were recorded to determine the optimum working potential; to this end 50 ng of the pesticide solution was injected into the HPLC system while the potential of the working electrode was scaled down from +1.3 V to +0.5 V. As the electroactivity of substances may be influenced significantly by irradiation with UV light, hydrodynamic measurements were carried out with and without photolysis. In the case of fenuron and neburon the signal intensity was reduced under photolytic conditions, whereas the acitivity of chlorotoluron and linuron remained constant. However, amperometric detection is possible at a working potential 0.5 V lower than without photolysis. To explain the respective reaction mechanism under photolysis, 1H-NMR studies were performed on the example of fenuron. To obtain efficient preconcentration of water samples a C18 solid-phase extraction system was applied, this resulted in good reproducibility and high recoveries. LOD's of the method developed are in the lower picomole range and meet the requirements of the European Community Drinking Water Directive concerning the limits for pesticides in ground and drinking water. Furthermore, this method has the advantages of being rapid, simple, highly selective and sensitive.