A direct competitive ELISA for the detection of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) has been developed. The optimization, evaluation and characterization of the ELISA, with two different antisera, has been carried out. The detection limit of 2,4-D with antiserum 7/89 was 20 ng/l and a center point value of 0.6 g/l 2,4-D. Antiserum 16/88 showed a detection limit of 0.3 g/l with a center point value of 4 g/l. The cross reactivity both at the center point and at the detection limit for five structural related phenoxycarboxylic acid herbicides has been determined. The influence of increasing concentrations of humic acid, solvents and surfactants on the ELISA has been investigated, leading to a deterioration of detection limits and center points.

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