Determination of microcystin variants and related peptides present in a water bloom of Planktothrix (Oscillatoria) rubescens in a Spanish drinking water reservoir by LC/ESI-MS.

A water bloom of Planktothrix (Oscillatoria) rubescens was observed in a drinking water reservoir in central Spain in 2003. Microcystins where analysed by LC/ESI-MS in 21 samples collected from this reservoir in five different days between March and May. A demethylated variant of microcystin-RR was identified as the major microcystin in most samples. Trace levels of microcystin-LR, -RR and -YR were detected in some samples. Four less common microcystins, with [M+H]+ ions at m/z 960, 981, 1045 and 1053, were also found. Total extracellular microcystin concentration varied from 0.010 to 19.126 microg l(-1). Furthermore, anabaenopeptins B and F as well as Oscillamide Y were also identified in these samples.