Study and determination of the pesticide Imidacloprid by square wave adsorptive stripping voltammetry

An electroanalytical method has been developed for the detection and determination of the pesticide 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2ylidineamine (Imidacloprid) by square wave adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE) in aqueous solution with Britton-Robinson buffer as supporting electrolyte. The best adsorption conditions were found to be pH 7.2, an accumulation potential of -1050 mV (HMDE vs. Ag/AgCl-KCl 3M) and an accumulation time of 50 s. Effects of square wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 x 10(-8)-5 x 10(-7) M with a detection limit of 1.6 x 10(-8) M (Clayton et al. method). The method is applied to the direct determination of the pesticide in river water samples. For a concentration of 4.1 x 10(-8) M a recovery value of 104+/-3% is obtained. In order to determine lower concentrations, previous preconcentration and cleaning steps (liquid-liquid extraction into CH(2)Cl(2) and solid-phase extraction with Sep-Pak C(18) cartridges) are carried out. The recovery values obtained in spiked river water are 89+/-4% for 2 x 10(-8) M and 90+/-6% for 8 x 10(-9) M.