DETERMINATION OF THE INSECT GROWTH-REGULATOR METHOPRENE IN WHEAT-GRAIN AND MILLING FRACTIONS USING AN ENZYME-IMMUNOASSAY

An improved enzyme immunoassay was developed for the insect growth regulator methoprene, and the assay was used to determine methoprene in whole wheat grain and milling fractions, including flours, whole meal, bran, and wheat germ. Either methanol or acetonitrile could be used to extract methoprene from grain, flours, and bran; no cleanup of extracts was required. Methanol produced less matrix effects and could be tolerated at higher concentrations in the assay. However, it was a poor extractant of methoprene from wheat germ, where acetonitrile gave more reliable results. The improved assay had a sensitivity of 250 pg/mL, and 50 % inhibition of antibody binding occurred at 3 ng/mL, corresponding to a maximum sensitivity of 60 ppb and 50 % inhibition of antibody binding at 0.75 ppm in the wheat sample when the routine assay method was used. The latter value is in keeping with residue levels typically found in methoprene-treated stored grain. Good correlations were found between methoprene determined in wheat and grain fractions by using the enzyme immunoassay and by conventional HPLC analysis.