Determination of spirotetramat and imidacloprid residues in cotton seed, lint, oil and soil by HPLC UV method and their dissipation in cotton plant.

A supervised field trial at four locations in India was conducted to establish the fate of residues of imidacloprid and spirotetramat in cotton, seed, lint, oil and soil following the application of a combinational insecticide formulation (480 SC) containing spirotetramat 12% and imidacloprid 36% w/w as active contents. The insecticide formulation was applied on cotton plant thrice at T1 - 750 ml ha−1 (spirotetramat 90 g and imidacloprid 270 g a.i. ha−1 and T2 -1500 ml ha−1 (spirotetramat 180 g and imidacloprid 540 g a.i. ha−1) with an interval of ten to twenty d between each application. The dissipation of insecticide residues on cotton plant was also studied by periodically collecting the leaf samples following one single foliar spray application of the formulation. Residues of spirotetramat and imidacloprid were quantified using a validated high performance liquid chromatography with UV detector (HPLC-UV) method. The method has the limit of detection 0.01 mg L−1 and the limit of quantification (LOQ) 0.03 mg kg−1 based on signal to noise ratio 3:1 and 10:1 respectively for all the molecules investigated. The residues of imidacloprid and spirotetramat on cotton plant dissipated to below the detectable level by tenth day. During the dissipation the formation of ‘enol’ metabolite of spirotetramat was observed and quantified. Analysis of all the four location samples collected at harvest showed no detectable residues of imidacloprid, spirotetramat and its metabolite enol in cotton lint, seed, oil and soil. The pre harvest interval was established as 25 d.