Liquid chromatography coupled to quadruple time‐of‐flight tandem mass spectrometry for microcystin analysis in freshwaters: method performances and characterisation of a novel variant of microcystin‐RR

Abstract

Cyanobacteria, also called blue-green algae, occur worldwide within water blooms in eutrophic lakes and drinking water reservoirs, producing several biotoxins (cyanotoxins). Among these, microcystins (MCs) are a group of cyclic heptapeptides showing potent hepatotoxicity and activity as tumour promoters. So far, at least 89 MCs from different cyanobacteria genera have been characterised. Herein, ion trap, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) and quadruple time-of-flight (Q-ToF) mass spectrometry (MS)-based methods were tested and compared for analysing MCs in freshwaters. Method performances in terms of limit of detection, limit of quantification, mean recoveries, repeatability, and specificity were evaluated. In particular, a liquid chromatography/electrospray ionisation (LC/ESI)-Q-ToF-MS/MS method was firstly described to analyse MCs in freshwaters; this technique is highly selective and sensitive, and allowed us to characterise the molecular structure of an unknown compound. Indeed, the full structural characterisation of a novel microcystin variant from a bloom of Planktothrix rubescens in the Lake Averno, near Naples, was attained by the study of the fragmentation pattern. The new cyanotoxin was identified as the 9-acetyl-Adda variant of microcystin-RR.

An integrated strategy for rapid and accurate determination of free and cell-bound microcystins and related peptides in natural blooms by liquid chromatography–electrospray-high resolution mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry using both positive and negative ionization modes

“…Negative ionization mode by MALDI and ESI presented low absolute intensities but also low background and therefore provided suitable S/N ratios. According to other authors [19][20][21]44], as shown Table S1 of supplementary data, the analysis of MCs containing no Arg residue such as MC-LA, -LF, -LW and -LY presented high sensitivity in negative ionization mode.…”

“…Combined MS techniques (accurate mass measurements, MS/MS and MS n experiments) and analytical techniques complementary to LC-MS such as thiol derivatization, chiral amino-acid analyses, nuclear magnetic resonance and ultraviolet-visible spectroscopy, or deuterium exchange experiments are useful for unambiguous structural identification and confirmation of cyanotoxins [44][45][46][47][48].…”

Hepatotoxic-Microcystins in Two Drinking Water Reservoirs in the Central Region of Ghana

“…The Italian Government has instituted a law setting 0.84 µg/L total microcystin as the tolerable limit in freshwater to prevent possible intoxication. 29 Addico et al 30 have earlier recorded a total intracellular microcystin concentration of 3.21 µg/L at the intake of the Weija Reservoir. This value is much higher than the 0.79 µg/L obtained at the Brimsu Reservoir.…”

Development of a high sensitive automatic setup for screening of microcystins in surface waters by employing a LED-based photometric detector

“…Human illness and death associated with microcystin toxicity occurred among dialysis patients during 1996 in Caruaru, Brazil [1,8]. These papers showed that there is an awareness concerning the risk that aquatic organism, domestic animals and humans can be poisoned by microcystins delivered in water by the cyanobacteria [1,3,[9][10][11][12][13]. In response, the World Health Organization (WHO) has suggested a provisional guideline value of 1 g L −1 microcystins in drinking water [14].…”

“…Nevertheless, the preferred method has predominantly been liquid chromatography coupled to mass spectrometry [2,[10][11][12]14,17,18].…”