Effects of physicochemical variables and cyanobacterial extracts on the immunoassay of microcystin-LR by two ELISA kits

Two types of commercially available ELISA kits for the immunoassay of cyano bacterial microcystins were evaluated for potential interference effects du e to methanol, salinity, pH, plasticware and cyanobacterial extract. Of the treatments examined, methanol had the greatest effect, giving false positi ve microcystin concentrations with increasing methanol concentrations up to 30% (v/v) compared with the negative calibrators of each kit. False positi ve microcystin results were also produced with increasing salinity up to fu ll strength seawater. Decreases in microcystin-LR equivalents were observed when assaying purified microcystin-LR at pH values between 6.25 and 10. Aq ueous microcystin-LR solutions in plastic microcentrifuge tubes after pipet ting with disposable plastic tips had lower toxin concentrations than expec ted when analysed by ELISA. Indicated microcystin concentrations in cyanoba cterial extracts varied between kit types and the choice of blanks used. Al though ELISAs can be useful tools for the screening of water and cyanobacte rial blooms for microcystins and nodularins, users should be aware that com mercial kits can be susceptible to interference by commonly encountered env ironmental and laboratory conditions and materials.