Development of an enzyme-linked immunosorbent assay for the herbicide bentazon

An ELISA method for the herbicide bentazon was developed. The approach to hapten synthesis addressed the problem of the presence of an ionizable NH group. Three immunogens were used to induce polyclonal antibodies toward bentazon and its derivatives in rabbits. One immunogen with a haptenic spacer at the sulfonamide NH of bentazon provided specific and sensitive antibodies to bentazon derivatives. The antibodies against succinylated KLH linked to bentazon through the NH showed very low affinity to bentazon and its derivatives. The third immunogen with a haptenic spacer at the aromatic ring of bentazon failed to induce bentazon-specific antibodies. The sensitivity and specificity of the resulting assays were investigated with different combinations of bentazon derivatives as immunogens and coating antigens. Solid-phase extraction and derivatization were employed to increase assay sensitivity. Detection limits for N-ethylated and N-methylated bentazon ranged from 0.01 to 0.1 μM (2-24 ppb of bentazon equivalent) in assay buffer. Gas chromatography (GC) was used as a comparison test to validate the ELISA procedure for N-methylbentazon. The correlation between data from GC and ELISA analyses was 0.95 with a slope of about 1.0.