Development of an enzyme immunoassay for metsulfuron-methyl

The development of an indirect competitive ELISA for the highly effective sulfonylurea herbicide metsulfuron-methyl (MSM) is described. As hapten, only the methylester phenylsulfonamide of MSM with an additional succinic acid spacer was used. It was coupled to carrier proteins by the activated ester method. Antibodies raised in rabbits were screened for sensitivity and specificity for MSM. Using an antiserum dilution of 1:180 000 and a coating antigen (hapten-BSA) concentration of 0.5 ng ml^-1 the IC₅₀ values achieved for the target analyte were in the 1.4 μg l^-1 range, with the limit of detection being 40 ng l^-1. The anti-MSM antibodies cross-reacted mainly with sulfometuron (43%), cinosulfuron (16%) and triasulfuron (10%) and, to a much lower extent, with a few other sulfonylureas. The influence of potential matrix interferences such as organic solvents, humic acids and surfactants was investigated. Gas chromatography (GC) was used as a comparison test to validate the ELISA with fortified water samples. The correlation between data from GC and ELISA analyses was 0.995 (n = 9) with a slope of 1.03.