Enhanced LC-MS analysis of microcystins via thiol derivatization—enhanced LC-MS analysis of microcystins via thiol derivatization

Summary

Mercaptoethanol and MEMHEG react rapidly and efficiently with [Mdha7]- and [Dha7]-containing microcystins, adding 78 and 356 Da, respectively, to their molecular masses (1). LC-MS analysis of samples before and after treatment reveals characteristic mass changes for these types of microcystins, providing added confidence to the identity of putative microcystin peaks. Comparison of fragmentation spectra of microcystin analogues before and after derivatization can also facilitate identification of putative structures via the characteristic change in mass of the [Mdha]-containing fragments. [Dhb7]-containing microcystins react more than two orders of magnitude more slowly than their isobaric [Mdha7]-containing congeners. It is therefore possible to rapidly and conveniently differentiate [Mdha7]- and [Dhb7]-microcystins in the same sample using this approach. The thiol-derivatization method provides a flexible strategy for analysis of microcystins by LC-MS, even in complex matrices and without access to MS/MS-capability. We illustrate the potential of this strategy by analysing bloom and culture samples from southern Africa and Scandinavia. These include samples from Tanzania (Lake Victoria), South Africa (Hartbeespoort Dam) (both Microcystis spp.), and Norway (Lake Steinsfjorden) (Planktothrix spp.). 1. Miles, C. O.; Sandvik, M.; Nonga, H. E.; Rundberget, T.; Wilkins, A. L.; Rise, F.; Ballot, A., Thiol derivatization for LC-MS identification of microcystins in complex matrices. Environ. Sci. Technol. 2012, 46, 8937−8944.