Monoclonal antibodies specific for the organophosphate pesticide azinphos‐methyl

2‐(2‐Mercapto‐5‐methyl‐1,3,2‐dioxaphosphorinan‐5‐yl,2‐sulphide)methoxyacetic acid has been synthesized and used to prepare an azinphos hapten and protein conjugates. Monoclonal antibodies of high affinity against the pesticide azinphos‐methyl were prepared from mice immunized with the hapten‐ovalbumin conjugate. The best monoclonal antibody could be used in an indirect enzyme‐linked immunosorbent assay (ELISA) to quantify azinphos‐methyl at concentrations from 50 pg ml‐1 to 2 ng ml‐1 (2.5–100 pg/assay). The corresponding limit of detection of the pesticide was less than 40 pg ml‐1. Only the closely related pesticide azinphos‐ethyl showed any appreciable cross‐reactivity in this assay.