Direct online quantitation of 2-methyl-3-methoxy-4-phenyl butanoic acid for total microcystin analysis by condensed phase membrane introduction tandem mass spectrometry

Microcystins (MCs) are a potent class of hepatotoxins produced by several species of cyanobacteria, which have been responsible for illness and death in livestock and humans. Rapid detection and quantitation are important for the protection of human and environmental health. More than 200 MC variants have been reported, and nearly all release 2-methyl-3-methoxy-4-phenyl butanoic acid (MMPB) upon oxidation. The quantitation of MMPB directly in complex post-oxidation solutions is presented using online condensed phase membrane introduction mass spectrometry with a methanol acceptor phase and negative electrospray ionization. We observe a linear response over several orders of magnitude for MMPB standards, and have applied the technique to measuring total MC in algal suspensions with both positive and negative controls. Preliminary results are reported for the analysis of total microcystins after Lemieux oxidation, at detection limits relevant to regulatory levels in recreational and drinking waters, with no sample clean up. Good quantitative agreement was obtained between measurement of total MCs in an algal reference material by CP-MIMS-MS/MS and LC-MS/MS analysis of total and free MCs. The developed methodology is of interest as an important first step for further development as a rapid benchtop tool for quantitative analysis with future potential use in the field.