Development of an indirect competitive immunoassay for parathion in vegetables

An indirect competitive immunoassay for the insecticide parathion has been optimized and characterized. This assay is based on a monoclonal antibody (2H₉) produced from an immunogen, a bovine thyroglobulin (BTG) conjugate wherein the reduced form of parathion was multiply bound to the carrier protein via diazo bonds. Assay was performed in the parathion-HSA coated (0.25 μg/ml) ELISA format in which antibody was diluted 1:2000. Several physicochemical factors (pH, ionic strength, BSA concentrations and organic solvent) that influence assay performance were studied and optimized. Finally, the assay was applied to the analysis of parathion in spiked vegetable samples. The sensitivity, estimated as the IC₅₀ value, was 360 ng/ml, with a practical working range between 47 and 6000 ng/ml, a limit of detection of 26 ng/ml, and inter-assay and intra-assay variations less than 10%. The average recovery of parathion added to potato, celery and Chinese cabbage were 173 ± 34%, 108 ± 15% and 98 ± 6%, respectively.