Multiclass cyanotoxin analysis in reservoir waters: Tandem solid-phase extraction followed by zwitterionic...

The presence of cyanobacteria and cyanotoxins in all water bodies, including ocean water and fresh water sources, represents a risk for human health as eutrophication and climate change are enhancing their level of proliferation. For risk assessment and studies on occurrence, the development of reliable and sensitive analytical approaches able to cover a wide range of cyanotoxins is essential. This work describes the development of an HILIC-MS/MS multiclass method for the simultaneous analysis of eight cyanotoxins in reservoir water samples belonging to three different classes according to their chemical structure: cyclic peptides (microcystin-LR, microcystin-RR and nodularin), alkaloids (cylindrospermopsin, anatoxin-a) and three non-protein amino acids isomers such as β-methylamino-L-alanine, 2,4-diaminobutyric acid and N-(2-aminoethyl)glycine). A SeQuant ZIC-HILIC column was employed to achieve the chromatographic separation in less than 12 min. Previously, a novel sample treatment based on a tandem solid-phase extraction (SPE) system using mixed cation exchange (MCX) and Strata-X cartridges was investigated with the aim of extracting and preconcentrating this chemically diverse group of cyanotoxins. The Strata-X cartridge, which was configured first in the line of sample flow, retained the low polar compounds and the MCX cartridge, which was at the bottom of the dual system, retained mainly the non-protein amino acids. The optimization procedure highlighted the importance of sample ion content for the recoveries of some analytes such as the isomers β-N-methylamino-L-alanine and 2-4-diaminobutyric acid. Method validation was carried out in terms of linearity, limit of detection (LOD) and quantification (LOQ), recoveries, matrix effect and precision in terms of repeatability and intermediate precision. This work represents the first analytical method for the simultaneous analysis of these multiclass cyanotoxins in reservoir water samples, achieving LOQs in the very low range of 7·10^-3 - 0.1 μg L^-1. Despite high recoveries obtained at the LOQ concentration levels (101.0-70.9%), relative standard deviations lower than 17.5% were achieved.