Cereal Chem. 71:107-111   |  VIEW ARTICLE


Immunoassay Detection of Herbicide Residues in Corn.

C. L. Hardy and C. R. Hurburgh, Jr. Copyright 1994 by the American Association of Cereal Chemists, Inc. 

Immunoassay detection kits were used to detect herbicide residues in spiked corn samples. Five herbicide compounds (atrazine, alachlor [Lasso], metolachlor [Dual], cyanazine [Bladex], and 2,4- dichlorophenoxy acetic acid [2,4-D]) commonly used by corn producers were selected as analytes. Selection was based on a survey of 200 Iowa Corn Grower Association members. Commercial test kits for water analysis for these compounds were available from Ohmicron Corporation, Newtown, PA. Two extraction methods, blender and heated shaker, were compared for efficiency of herbicide recovery at three spike levels. The blender method yielded recoveries of 80-100% of herbicide spike in the immunoassay for all compounds. Recoveries from the heated shaker method were comparable for four of the five compounds. Low detection limits for the immunoassay in corn were 20 ppb, with greater variability near the low end of the calibration. Variability decreased with increasing levels of herbicide spike. Recoveries on selected spiked samples were confirmed by traditional detection methods. Blank adjustments were made to compensate for the interferences caused by the corn. Iowa farmers provided 200 corn samples and accompanying two-year herbicide usage history. These samples were assayed for the five compounds, using the immunoassay test kits. Herbicide usage patterns were close to those reported in Iowa and Illinois industry data. No samples tested positive for atrazine, alachlor, metolachlor, or cyanazine. There were two positive, above-tolerance results, not confirmed by chromatography, for 2,4-D. The immunoassay required 0.5 hr of labor per sample in addition to the cost of the kit.