Towards an Automated Untargeted Method for Microcystins Analsysi using 2D-LC and Ion Mobility Quadrupole Time of Flight Mass Spectrometry

Topics in Drinking Water
Oral Presentation

Presented by K. Rosnack
Prepared by A. Ladak1, X. Ortiz2, L. Mullin1, K. Rosnack1
1 - Waters Corporation, 34 Maple Street, Milford, MA, 01757, United States
2 - Ministry of the Environment and Climate Change, 4905 Dufferin Street, Toronto, Ontario, M3H 5T4, Canada


Contact Information: adam_ladak@waters.com; 508-482-4664


ABSTRACT

Microcystins are cyclic heptatpeptide hepatotoxins produced by certain species of cyanobacteria (blue-green algae) found in freshwater environments. These secondary metabolites are toxic to higher organisms, causing human sickness or even death in some cases. There are only a handful of microcystin standards available in the market and over 90 different microcystins variants have been reported. For this reason, it is important to develop non-targeted methods for the analysis of these compounds.
An automated method for microcystins extraction and clean up from water samples was developed using 2D-LC in the trap and elute configuration: a large volume of water sample (500 Ál) was directly injected and trapped in the first column. After that, microcystins were desorbed in reverse flow and injected to the analytical column, prior to mass spectrometry analysis.
When the QTof-MS was operated in high resolution full scan mode (RP ? 25,000), the instrument proved to be very sensitive for microcystin-LR (50 fg on column with S/N > 10). Combined with the 2D-LC, the system could detect 100 pg/L of microcistyn-LR in water with S/N>10. Mass accuracy (< 1 ppm) allowed assigning elemental compositions for unknown compounds with confidence. MS/MS mode monitoring the characteristic microcystin ion at m/z=135.0804 was useful to provide quantitative results of targeted compounds in complex samples.
For a more comprehensive characterization of complex algal bloom samples, ion mobility was used to distinguish the different microcystin variants based on their collisional cross-section. This new dimension of separation allowed the identification of some congeners that could not be separated by means of chromatography or mass spectrometry alone. Advanced acquisition methods such as Data Dependant Acquisition (DDA) and Data Independent Acquisition (DIA) were successfully employed to elucidate new microcystin variants in real samples that have not been reported in literature yet.