Fast screening of saxitoxin, neosaxitoxin, and decarbamoyl analogues in fresh and brackish surface waters by on-line enrichment coupled to HILIC-HRMS.

The proliferation of harmful cyanobacterial algal blooms is of concern due to the associated release of toxins affecting ecosystems and human health. The paralytic shellfish poison saxitoxin (STX) is a small polar alkaloid that can occur in inland and marine aquatic environments. Here, we optimized a fast and sensitive analytical method for the determination of STX, neosaxitoxin (NeoSTX), and their decarbamoyl analogues in surface waters. The method involves a simple filtration, addition of isotope-labelled internal standard (ILIS), and analysis by on-line solid-phase extraction coupled to hydrophilic interaction liquid chromatography high-resolution mass spectrometry (on-line SPE–HILIC-HRMS). Except glass fiber filters, other tested materials (e.g., nylon, nitrocellulose) provided suitable filtration performance. Time-dependent adsorptive losses occurred during the LC-MS batch sequence if glass autosampler vials were used, while no such effect was observed for polypropylene autosampler vials. Matrix effects were evaluated for 4 different quantification scenarios, including external vs. internal curves and neat reagent water vs. matrix-matched curves. Matrix-matched calibration with ILIS correction (NeoSTX-15N 7) provided the best performance overall. The analytical method was validated in freshwater lake water and estuarine brackish water (30‰ salinity), with suitable determination coefficients (R2 > 0.9975), matrix spike accuracy (90–107%), and intraday/interday precision (RSD of 0.61–16%). Method limits of detection (LOD in lake water: 0.72–3.9 ng/L) are also improved over most of the recent literature. The method was applied to a set of 302 surface water samples collected in Canada, France, and the United Kingdom, and positive detections were reported for STX (max: 98 ng/L), decarbamoyl-STX (max: 15 ng/L), and NeoSTX (max: 87 ng/L). [Display omitted] • A rapid method to analyze paralytic shellfish toxins in surface water is reported. • On-line SPE coupled to HILIC-HRMS yielded LODs of 0.72–3.9 ng/L in lake water. • Glass was avoided for filters & HPLC autosampler vials due to adsorptive losses. • Saxitoxins were screened in 302 samples of Canada, France, and the United Kingdom. • Saxitoxin and neosaxitoxin were detected in freshwater and saltwater field samples. [ABSTRACT FROM AUTHOR]