| dc.description |
Microcystins are a group of cyclic heptapeptides
originating from cyanobacteria. Cyanobacteria also
produce a range of peptides and other compounds that can
result in complex chromatograms when samples are analyzed
by LC-MS. Derivatization with appropriate thiols (e.g.,
mercaptoethanol) of the olefin in the α,β-unsaturated amide
present in most microcystins was shown to simplify analysis of
LC-MS chromatograms of sample extracts, making it much
easier to identify peaks corresponding to candidate microcystins. Furthermore, interpretation of MS2 spectra was facilitated by
addition of the mass associated with the thiol to the α,β-unsaturated amide of microcystins. Cyanotoxins containing Mdha or
Dha reacted readily with thiols, whereas Mser, Ser, Mdhb, and thiol-derivatives of Mdha or Dha did not react under the
conditions used. This approach therefore provides a convenient LC-MS method to obtain evidence for the presence of Mdha or
Dha and can likely be used to differentiate between the isobaric amino acids Mdha and Dhb in candidate cyanotoxin peaks. When
O-(2-mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (MEMHEG) (Mwt. 356) was used as the thiol, the resulting derivatives
eluted in an LC-MS mass window that was largely free of interferences. This approach simplifies detection of candidate
microcystin analogues even in the presence of complex mixtures of coeluting components. The method was used for qualitative
analysis of a Microcystis aeruginosa culture from Lake Naivasha, Kenya, and the results were verified using precursor-ion scanning
and high-resolution mass spectrometry. |
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