Evaluation of an ELISA kit for the monitoring of microcystins (cyanobacterial toxins) in water and algae environmental samples

A recently developed commercial microtiter plate ELISA test kit for microcystins was evaluated for its reproducibility, accuracy, detection limits in real samples, and comparability to results obtained from solid-phase extraction followed by liquid chromatography. Detection limits in the deionized water matrix were 0.05 mu g/L, and the overall intra- (two to five replicates) a nd interkit (th ree replicates) reproducibility at this level was good (%CV < 10%). Various types of groundwater and surface water samples gave a matrix effect at low concentration levels so that limits of detection were obtained in the range 0.1-0.15 mu g/L with the possibility of obtaining a false positive in this range. The limits of quantification were measured at 0.2 mu g/L in several types of surface water samples. A fast and simple enrichment step using disposable C18 cartridges allows lower detection limits and is recommended in order to avoid a false positive. No false negative measurements were detected. Reliable correlations between measurements obtained by ELISA and by solid-phase extraction followed by liquid chromatography were obtained in spiked drinking and surface water samples (n = 8, r(2) = 0.989). In algae samples, the occurrence of several microcystins which may crossreact was shown using mass spectrometry but could not he confirmed due to the lack of commercially available standards. Overall, the assay illustrated the ability to measure concentrations of microcystins-LR and -YR in the range 0.2-4 mu g/L in any type of surface water, allowing thus rapid and on-site detection of toxins in cyanobacterial blooms without any pretreatment.