Rapid quantitative analysis of microcystins in raw surface waters with MALDI MS utilizing easily synthesized internal standards

Abstract

The freshwater cyanotoxins, microcystins (MCs), pose a global public health threat as potent hepatotoxins in cyanobacterial blooms; their persistence in drinking and recreational water has been associated with potential chronic effects in addition to acute intoxications. Rapid and accurate detection of the over 80 structural congeners is challenged by the rigorous and time consuming clean up required to overcome interference found in raw water samples. MALDI-MS has shown promise for rapid quantification of individual congeners in raw water samples, with very low operative cost, but so far limited sensitivity and lack of available and versatile internal standards (ISs) has limited its use. Two easily synthesized S-hydroxyethyl–Cys(7)-MC-LR and –RR ISs were used to generate linear standard curves in a reflectron MALDI instrument, reproducible across several orders of magnitude for MC –LR, - RR and –YR. Minimum quantification limits in direct water samples with no clean up or concentration step involved were consistently below 7 μg/L, with recoveries from spiked samples between 80 and 119%. This method improves sensitivity by 30 fold over previous reports of quantitative MALDI-TOF applications to MCs and provides a salient option for rapid throughput analysis for multiple MC congeners in untreated raw surface water blooms as a means to identify source public health threats and target intervention strategies within a watershed. As demonstrated by analysis of a set of samples from Uruguay, utilizing the reaction of different MC congeners with alternate sulfhydryl compounds, the m/z of the IS can be customized to avoid overlap with interfering compounds in local surface water samples.

Simultaneous Detection of 14 Microcystin Congeners from Tissue Samples Using UPLC- ESI-MS/MS and Two Different Deuterated Synthetic Microcystins as Internal Standards

“…The quantification method presented here using two synthetic deuterated MCs as internal standards is, to the best of our knowledge, the first time this has been carried out for MCs. Previous studies have either employed MC-LR with an attached thiol group at the Mdha residue as an internal standard for the HPLC-MS analysis of MC-LR, -RR and -LA [27], or similarly thiolised MC-LR and -RR in conjunction with MALDI-MS [26]. The problem with the latter approach is that thiolised internal standards do not necessarily have the same behaviour during extraction and analysis as the parent compounds.…”

“…Unfortunately, appropriate internal standards are still missing. Quantitation from various samples using ISs has been attempted previously [20,26,27]. However, in these approaches, either nodularin or thiolised MC-LR/-RR at the Mdha moiety was employed.…”

The end user sensor tree: An end-user friendly sensor database

“…An interesting development for non-portable quantitative detection methods is replacing chromatography by direct MS measurements. Indeed, some MS techniques showing sensitive and quantitative analysis without applying chromatography beforehand for aquatic toxin detection using either matrix assisted laser desorption ionisation (MALDI) (Roegner et al, 2014) or ambient source high resolution MS solutions (Roy-Lachapelle et al, 2015) when compared to classic triple quadrupole LC-MS (Pekar et al, 2016). Evidently, such systems can speed up analysis and enable rapid screening in the lab using non-portable devices, an alternative to the point-of-site solution.…”

Oriented Functionalization of Magnetic Beads with in Vivo Biotinylated Nanobodies for Rapid MALDI-TOF MS Ultrasensitive Quantitation of Microcystins in Biological Samples

“…The IS was prepared by reaction of MC-YR with β-mercaptoethanol as described before . Briefly, 250 μL of 0.1 μM MC-YR dissolved in 50% methanol/50% 100 mM borate buffer, pH 10.5 was reacted with 10 μL of β-mercaptoethanol for 6 h at room temperature under nitrogen.…”