Microcystins are a group of toxins produced by cyanobacteria that consists of a seven-membered peptide ring made up of five non-protein amino acids and two protein amino acids. Microcystins differ from each other depending on the two protein amino acids located at the “X” and “Z” amino acid positions. One of the most commonly detected is microcystin-LR, in which there is a leucine (L) and arginine (R) amino acid located in these two positions. There are approximately 80 known variants of microcystins, but the prospect of other variants exists due to the numerous combinations possible from available amino acids. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) detection is a commonly employed analytical method for low level detection of known microcystins variants. However, only a handful of microcystin variants are available to purchase as standards making them difficult and limiting to analyze for in unknown water samples. This research centers around the use of advanced LC-MS/MS techniques along with triggered information dependent acquisition (IDA) to screen water samples for microcystins in a non-targeted fashion. This is accomplished by first identifying common fragments, or product ions, using precursor scan methods. One such common fragment is the β-ADDA amino acid group which will break off the parent molecule regardless of the varying amino acids in the “X” and “Z” positions. Upon detection, the instrument triggers an enhanced resolution scan of the corresponding precursor ion which gives relevant information regarding the molecular weight of the unknown microcystin. Using this technique, non-targeted microcystins can be initially detected and the obtained information used to determine possible forms. Screening methods have been developed and optimized using ESI positive and negative for both single and double charged microcystins. This method utilizes direct injection and therefore, requires no sample prep for screening tests and also does not require any previously purchased standards. Screening methods were tested on water samples with known microcystins and unknown environmental samples.

Microcystin screening in water samples using LC-MS/MS and triggered information dependent acquisition for non-targeted variant detection

253rd National Meeting (2017)

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