Enhanced sample preparation for quantitation of microcystins by matrix-assisted laser desorption/ionisation-time of flight mass spectrometry

Microcystins (MCs) are a group of cyanotoxins which pose a serious health threat when present in aquatic systems. Quantitative analysis of MCs by matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry has potential for the processing of large numbers of samples quickly and economically. The existing method uses an expensive internal standard and protocols that are incompatible with automated sample preparation and data acquisition.

To produce a MALDI-TOF sample preparation technique for the quantitation of MCs that not only maintains reproducibility and sensitivity, but is also compatible with an automated work-flow.

Seven different MALDI-TOF sample preparations were assessed for signal reproducibility (coefficient of variation) and sensitivity (method detection limit) using a cost-effective internal standard (angiotensin I). The best preparation was then assessed for its quantitative performance using three different MC congeners ([Dha⁷] MC-LR, MC-RR and MC-YR).

The sensitivity of six of the preparations was acceptable, as was the reproducibility for two thin-layer preparations performed on a polished steel target. Both thin-layer preparations could be used with a MALDI-TOF mass spectrometer that automatically acquires data, and one could be used in an automated sample preparation work-flow. Further investigation using the thin-layer spot preparation demonstrated that linear quantification of three different MC congeners was possible.

The study demonstrates that with different sample preparation methods and modern instrumentation, large numbers of samples can be analysed rapidly for MCs at low cost.