Abstract: An immunoassay directed at certain analytes that have benzene rings, such that the immunoreactive standard used is less volatile than the analyte, and kits for performing the assay.

Abstract: There is provided a standard for use in testing for captan in immunoassays. This standard has the structure THPD--(CH.sub.2).sub.x --(R.sup.3).sub.y --R.sup.1 wherein THPD is cis-1,2,3,6-tetrahydrophthalimido, x is an integer from 1 to 10, R.sup.1 selected from the group consisting of --COOH, --NH.sub.2, --NO.sub.2, --SH and --OH, R.sup.3 is an aryl moiety and y is 0 or 1. Compounds of this general structure are known, they mimic the immunological reaction of captan and related compounds which are not stable in water and thus cannot be satisfactorily used as standards in testing for the presence and level of presence of captan and related compounds. There is also provided a method of carrying out such testing, utilizing such standards in which the standard (I) is coupled to a protein that is large enough to elicit an immune response in warm blooded animals, to yield compound (II). THPD--(CH.sub.2).sub.x --(R.sup.3).sub.y --R.sup.