DEVELOPMENT OF AN ENZYME-IMMUNOASSAY FOR METSULFURON-METHYL

The development of an indirect competitive ELISA for the highly effect ive sulfonylurea herbicide metsulfuron-methyl (MSM) is described. As h apten, only the methylester phenylsulfonamide of MSM with an additiona l succinic acid spacer was used. It was coupled to carrier proteins by the activated ester method. Antibodies raised in rabbits were screene d 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 mu g 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 int erferences such as organic solvents, humic acids and surfactants was i nvestigated. Gas chromatography (GC) was used as a comparison test to validate the ELISA with fortified water samples. The correlation betwe en data from GC and ELISA analyses was 0.995 (n = 9) with a slope of 1 .03.