Determination of imidacloprid and its major metabolite in soils by liquid chromatography with pulsed reductive amperometric detection

A liquid chromatography method assay for imidacloprid insecticide and its major metabolite 6-chloronicotinic acid was developed to monitor both compounds in soils. The electrochemical study of the compounds proves the reduction and adsorption processes on the mercury electrodes. Pulsed amperometric detection overcomes electrode fouling problems by repeatedly and continuously applying cleaning potentials to the working electrode. The measurement potential was -1300 mV and the cleaning and conditioning potentials were -500 and -1150 mV, respectively. The chromatographic separation was achieved on a Spherisorb CN column 5 mu m (4.1x250 mm). Samples were eluted with a mobile phase containing 5x10(-3) M phosphate buffer-acetonitrile (75 : 25), pH 2.5 at a flow rate of 1.0 mi min(-1). The limit of detection for this method was 2.7 ng of imidacloprid and 8.1 ng of 6-chloronicotinic acid.