Different techniques for determination of imidacloprid insecticide residues

Three sensitive, selective and precise methods for determination of imidacloprid insecticide residues in tomatoes have been developed. The first method is TLC-Densitometry where imidacloprid was extracted with acetonitrile without the need for a clean up step then the extract was applied to TLC plates using toluene: acetonitrile (7:3) as a solvent system. The recoveries ranged from 92.57 to 96.31% in tomato samples. The limit of detection of the method was 1.39 mg/kg. The second method depends on indirect fluorimetric determination of imidacloprid by quenching anthracene synchronous fluorescence. The recoveries ranged from 96.16 to 99.83% in tomato samples. The limit of detection of the method was 0.32 mg/kg. The third method is high-performance liquid chromatography with UV detection where imidacloprid was extracted with acetonitrile followed by clean up using column chromatography. The recovery of imidacloprid in tomato samples ranged from 85.20 to 93.15%. The limit of detection of the method was 0.12 mg/kg. The three methods were used to study the kinetic disappearance of imidacloprid from tomatoes. It was found to follow a first order reaction with t1/2 = 5.31 ± 0.3 days, whereas K (reaction rate constant) was found to be 0.13 ± 0.008 day−1.