Solid-phase fluoroimmunoassay for the determination of mesotrione--a novel triketone herbicide--in water with direct measurement of the fluorescence onto the solid support.

A straightforward, low-cost fluoroimmunoassay (FIA) for the determination of the new triketone herbicide mesotrione has been developed and optimized. The protein-mesotrione conjugate, immobilized on white opaque microtitration wells competes with the mesotrione in the sample or standard for the limited binding sites of a liquid phase anti-mesotrione antibody. The assay is based on the measurement of fluorescence intensity directly onto the solid support, using a fluorescein labeled second antibody and a fluorescence plate reader. To stabilize and enhance the fluorescence signal a glycerine-based treatment of the microtitration wells was included in the protocol. The detection limit of the assay is 40 ng 1(-1) (4 pg per well), the working range extends up to 9 microg l(-1), whereas the within and between run CVs are 0.7-4.2% and 2.1-5.5%, respectively. To evaluate the assay specificity, the cross-reactivities of two mesotrione metabolites: 4-methylsulfonyl-2-nitrobenzoic acid and 2-amino-4-methylsulfonyl-benzoic acid and several other compounds similar in structure to mesotrione such as: fomesafen, prosulfocarb, fluazinam, sulcotrione, 1,2-cyclohexanedione, 1,3-cyclohexanedione, 2-acetyl-1,3-cyclohexanedione were assessed. Most of the substances tested presented very low ( < 0.05%) cross-reactivity values with the exception of sulcotrione that cross-reacted 23% in the mesotrione assay. The assay was used for the determination of mesotrione in bottled natural waters fortified with the analyte and in a commercial herbicide formulation, namely CALLISTO.