Fast and Accurate Determination of Algal Toxins in Water Using Online Preconcentration and UHPLC-Orbitrap Mass Spectrometry

Significance of the Topic

Algal toxins produced by cyanobacteria pose serious health risks to humans and animals, requiring reliable monitoring of water supplies in compliance with WHO guidelines. Rapid and sensitive analysis methods are essential for early warning and management of drinking water sources.

Objectives and Study Overview

The study aimed to develop a fast, accurate column-switching method combining online preconcentration with high-resolution full-scan Orbitrap mass spectrometry for quantifying microcystin variants (LR, RR, YR) and nodularin in raw and treated water.

Methodology and Used Instrumentation

The method used 1 mL water injections into a Thermo Scientific EQuan MAX online UHPLC system. A Hypersil GOLD aQ trap column captured toxins under 98:2 water/acetonitrile with 0.1% formic acid, then switched to a Hypersil GOLD analytical column for elution. Detection was performed on a Thermo Scientific Exactive Orbitrap mass spectrometer in positive electrospray full-scan mode at 50 000 resolving power. Samples were filtered (0.45 µm GF) and analyzed within three days of collection.

Main Results and Discussion

Exact mass measurements and carbon isotope patterns confirmed toxin identities with high confidence. Retention times ranged 2.6–2.8 min. Calibration was linear over 100–1000 pg/mL (r² = 0.9971–0.9996), with reproducibility within ±15%. Online preconcentration achieved the same enrichment as offline SPE of 200 mL to 2 mL, but with only 1 mL injections. Analysis time per batch of five samples dropped from ~12.3 h (conventional) to ~2 h (online), an 80% reduction. Method detection limits were 0.009–0.035 ng/mL and quantitation limits 0.03–0.11 ng/mL. Recovery rates ranged 70.3–113.7% with precision 2.5–10.9%. Environmental samples from multiple river basins and treatment plants showed toxin levels below detection, while cyanobacterial concentrates revealed microcystin-LR.

Benefits and Practical Applications

• High-throughput screening with <5 min run times per sample
• Elimination of lengthy offline SPE reduces labor and solvent use
• Full-scan data enable retrospective analysis for non-target toxins
• Compliance with stringent international water quality limits

Future Trends and Potential Applications

Integration with automated monitoring networks and expansion to other cyanotoxins such as anatoxin and aplysiatoxin are promising. Advances in miniaturized UHPLC-Orbitrap platforms and data-driven retrospective screening will further enhance early warning capabilities.

Conclusion

The optimized online preconcentration UHPLC-Orbitrap method provides rapid, sensitive, and accurate detection of key algal toxins in water, significantly improving throughput and resource efficiency while meeting international safety guidelines.

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