Visual detection of cyanobacterial hepatotoxins by thin-layer chromatography and application to water analysis

Visualization reactions for the thin-layer chromatographic (TLC) analysis o f cyanobacterial hepatotoxins microcystins and nodularin were studied. Of t he 17 potential reactions tested, nine yielded either coloured, fluorescent , or both products with the purified toxins. The detection limit of pure mi crocystin-LR in these reactions ranged from 10 to 250 ng. Feasibility of th e reactions for water analysis was studied in fortified 50-500 ml water sam ples. The best result was obtained with N,N-dimethyl-1,4-phenylendiammonium dichloride (N,N-DPDD). A water analysis method meeting the WHO drinking wa ter guideline concentration value, 1 mu g/l of microcystin-LR, was develope d employing N,N-DPDD. The method was tested by analyzing blind 38 authentic natural water samples, studied earlier by the enzyme-linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PP). In 31 samples the results of all three methods were consistent. Two apparently false posi tive results were obtained by TLC, and in two samples results were positive by ELISA and TLC but not PP. In one sample the result was positive by PP b ut not ELISA or TLC. Two samples were positive by ELISA and PP and not TLC, but a full 50 ml sample for TLC was not available in these cases, thus mak ing the detection limit higher. Results suggest that the present TLC method is comparable with the ELISA and PP assays, and TLC can be used for cost-e ffective monitoring of water samples according to the WHO guidelines. (C) 2 000 Elsevier Science Ltd. All rights reserved.