Blue-green algae generate microcystins which are cyclic heptatpeptide hepatotoxins produced by certain species of cyanobacteria found in freshwater environments. These secondary metabolites are toxic to higher organisms, causing human sickness or even death in some cases. As they are produced in fresh water and brackish water, they can contaminate drinking water supplies. The WHO guideline limit for the most common microcystin, microcystin-LR is used in many countries. It includes a provisional value of 1 μg/L in drinking-water, and 10 μg/L for recreational exposure for total microcystin-LR (free plus cell-bound).

There are approximately 100 different microcystins variants that have been reported in literature. These variants are produced by the substitution of the seven amino acids. As regulations are constantly changing and the fact that other microcystins may have a similar toxic effect as the regulated LR, it is important to develop targeted and untargeted methods for the analysis of these compounds. 

In this application note, we describe a method that utilizes a combination of LC and high resolution mass spectrometry (HRMS) to perform targeted screening of microcystins in lake water samples. Alongside the samples, a calibration curve of microcystin-LR was acquired to perform quantitation. The combination of accurate mass data for both precursor and fragment ions in a single analysis with Xevo G2-XS QTof, and high quality UPLC separations was used to identify targeted compounds. As the data were acquired using a data-independent approach, additional compounds that were not included at the time of the initial analysis could also be investigated.