Development of Column-Switching LC-MS/MS Method for Rapid and Simultaneous Determination of Multiclass Cyanotoxins in Aqueous Samples

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Abstract
Multiclass cyanotoxins often co-occur in aquatic environments, but their broad structural and polarity ranges make comprehensive analysis difficult using a single chromatographic method. Here, we have developed a single-workflow column-switching liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous analysis of 36 cyanotoxins in aqueous samples with minimal sample preparation. The method combines large-volume injection, enrichment on a porous graphitic carbon (PGC) trap column, and valve switching with two complementary separation modes: reversed-phase (RP) chromatography and hydrophilic interaction liquid chromatography (HILIC). The moderately polar cyanotoxins were retained and separated on an RP column, whereas highly hydrophilic paralytic shellfish toxins (PSTs) that were poorly retained by RP separation were captured by the trap cartridge and subsequently transferred to a HILIC column for separation. This configuration substantially improved chromatographic retention and enhanced PST signal-to-noise ratios by up to 40-fold compared with direct RP analysis. Method quantification limits of all target cyanotoxins were ≤ 15 ng L-1 for freshwater matrices and ≤ 30 ng L-1 for seawater matrices. Matrix effects were modest in freshwater for 500 µL injection volume, whereas seawater caused stronger ion suppression that was mitigated by reducing the injection volume to 200 µL. The method accuracies (spike recoveries) of all tested cyanotoxins ranged from 82.5 to 117.0% for freshwater and 79.0 to 119.0% for seawater samples. Overall, this automated RP–PGC–HILIC column-switching platform provides a sensitive and high-throughput strategy for multiclass cyanotoxin monitoring across diverse water matrices.

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