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 microcy stins was evaluated for its reproducibility, accuracy, detection limits in real samples, and comparability to results obtained from solid-phase extrac tion followed by liquid chromatography. Detection limits in the deionized w ater matrix were 0.05 mu g/L, and the overall intra- (two to five replicate s) 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 en richment step using disposable C18 cartridges allows lower detection limits and is recommended in order to avoid a false positive. No false negative m easurements were detected. Reliable correlations between measurements obtai ned by ELISA and by solid-phase extraction followed by liquid chromatograph y 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 du e to the lack of commercially available standards. Overall, the assay illus trated 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 an d on-site detection of toxins in cyanobacterial blooms without any pretreat ment.