Determination of pesticide diafenthiuron by square wave stripping voltammetry

A square wave cathodic stripping voltammetric (SWCSV) method using static hanging mercury drop electrode (SHMDE) has been developed for the determination of insecticide diafenthiuron. The voltammetric procedure is based on controlled accumulation of the insecticide at the potential of ? 0,00 mV ( vs. Ag/AgCl) in Britton -Robinson buffer ( pH 7,0). Following this, the accumulated insoluble mercury-compound was reduced during the cathodic potential scan at ? 510 mV versus Ag/AgCl. The variation in pH and square wave parameters indicated that the optimum conditions under which diafenthiuron could be determined were a pH of 7,0, an accumulation potential of ? 0.00 mV, a deposition time of 220 s, a frequency of 350 Hz, a pulse amplitude of ? 200 mV, and staircase step of 15 mV. The peak currents obtained from voltammograms were linearly related to insecticide concentration between 30,4 and 3200 ? g L-1 . The observed values of detection limit (LOD) and quantification limit (LOQ) were 9,1 ? g L-1 and 30,4 ? g L-1, respectively. The proposed analytical procedure was applied to tap water and soil samples. The mean results for three determinations were 39,6 ± 2,5 ? g L-1, which is very close to the diafenthiuron added soil (40 ? g L-1), with a recovery of 99,0 %. The method was extended to the direct determination of diafenthiuron in agrochemical insecticide formulation Polo® 50 WP and average content of 50.3 ± 1,7 (n = 4, at 90% confidence level), in close agreement with the 50 % quoted by the manufacturer. Accuracy was in agreement with that obtained by HPLC comparison method. The influences of some pesticides and various ions as potential interfering, were also tested.