Varied influence of microcystin structural difference on ELISA cross-reactivity and chlorination efficiency of congener mixtures.

Enzyme-linked immunosorbent assay (ELISA) is an antibody-based analytical method that has been widely applied in water treatment utilities for the screening of toxic cyanobacteria metabolites such as microcystins (MCs). However, it is unknown how the minor structural difference of MCs may impact their chlorination kinetics and measurement via ELISA method. It was found in this study that, regardless of the experimental conditions (n = 21), there was no MC-YR or MC-LY residual, while different removal rates of other MCs were observed (MC-RR > MC-LR > MC-LA ∼ MC-LF) as measured by liquid chromatography tandem mass spectrometry (LC-MS/MS), which was consistent with the relative reactivity of the amino acid variables with free chlorine. The removal of total MCs was generally lower as measured by ELISA than by LC-MS/MS. By incorporating both analytical results, existence of ADDA-containing byproducts or byproducts that had a higher sensitivity toward the ELISA kit was demonstrated, after excluding the contribution of the cross-reactivity of the parent MCs. It should be noted, however, that the cross-reactivities of MCs could be influenced not only by MC congeners, but also by other conditions such as mixtures and the applied ELISA kit.