Accurate LC-MS analyses for microcystins using per-15N-labeled microcystins
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Per-15N-labeled microcystins were prepared for use as surrogates for accurate liquid chromatography–mass spectrometry analysis. Two strains of Microcystis aeruginosa were cultured in 15NO3-containing TS-15 medium. To change from the incorporation of 14N to 15N into all cell components, cells of Microcystis aeruginosa were precultured in Na15NO3-containing medium for more than 6 months. After mass cultivation of the strains, cells of each strain were harvested and lyophilized. Microcystin variants were extracted from the lyophilized cells and per-15N-labeled microcystin variants were purified using high-performance liquid chromatography and high-performance thin-layer chromatography. The structures of per-15N-labeled microcystin variants were confirmed by their mass spectrometry spectra and NMR spectra. When per-15N-labeled microcystins were used as surrogates for quantitative analysis of these toxins in cyanobacterial cells, excellent accuracy (98–106%) was obtained, with the m/z of M+, [M+1]+, and [M+2]+ of both microcystins and the per-15N-labeled microcystins as surrogates being completely separated. In conclusion, per-15N-labeled microcystins are excellent surrogates for microcystin analysis using liquid chromatography–mass spectrometry.
KeywordsMicrocystin Stable isotope Surrogate Liquid chromatography–mass spectrometry Accurate analysis
This study was supported by the Pollution Control Research Fund of the Ministry of the Environment (Japan).
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