Multianalyte effect in the determination of cross-reactivities of pesticide immunoassays in water matrices

An extension of Abrahamʹs method to calculate cross-reactivity (CR) is presented. Over a wide concentration range the response curves of a cross-reactant were compared with those of a standard applied to four immunoassay commercial kits (benomyl/carbendazim, chlorothalonil, metolachlor and parathion-ethyl). Various doses of cross-reactants (0–1000 μg/l) were tested in the presence of various doses of the standard (0–100 μg/l). The results showed that the percentage of the cross-reactivity (%CR) decreased as a function of the concentration of cross-reactant present in the water and high %CR values were found in comparison with those reported in commercial kits. This indicates a better sensitivity for many analytes as compared to values actually reported in the ELISA (Enzyme-Linked ImmunoSorbent Assay) kits. Applications of the CR studies are also presented that should help in the acceptance or rejection of a concentration range of cross-reactants in a real sample. When determining the CR in estuarine waters, the matrix effect of estuarine water underestimated the true extent of cross-reactivity of the standard, making it necessary to calculate for cross-reactivity to compensate for matrix effect.