Rapid and highly sensitive quantitation of Microcystins and Nodularin in water by modern LC-MS/MS

Importance of the Topic

Harmful algal blooms caused by cyanobacteria are increasingly common in nutrient-rich water bodies and pose a threat to drinking water sources and aquatic ecosystems. Cyanotoxins such as microcystins and nodularin can cause liver damage and other health issues at low concentrations. Rapid and sensitive detection of these toxins is essential to ensure environmental safety and compliance with regulatory limits set by organizations like the WHO and EPA.

Objectives and Study Overview

This study presents a fast and robust liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for simultaneous quantitation of six microcystin variants (MC-LR, MC-RR, MC-LA, MC-LF, MC-LY, MC-YR) and nodularin in water. The method follows EPA Method 544 guidelines and aims to improve sensitivity, linearity, and throughput without requiring extensive sample concentration steps.

Methodology

• Sample Preparation: Standards and samples prepared in 1:1 methanol/water with internal standard MC-LR-C2D5 at 25 μg/L.
• Chromatography: Shim-pack Velox SP-C18 column (2.1 × 100 mm, 2.7 μm) at 40 °C; 8-minute gradient from 15 % to 90 % organic mobile phase; flow rate 0.3 mL/min; injection volume 10 μL.
• Mass Spectrometry: Triple quadrupole LCMS-8060NX; electrospray ionization in positive mode; two MRM transitions per analyte; optimized interface and gas parameters for high sensitivity.

Instrumentation Used

• Shimadzu LCMS-8060NX triple quadrupole mass spectrometer.
• Shim-pack Velox SP-C18 column, 2.1 × 100 mm, 2.7 μm particle size.
• Electrospray ion source and multiple reaction monitoring (MRM) detection.
• Internal standard: MC-LR-C2D5.

Main Results and Discussion

• Separation and Sensitivity: Baseline separation of seven cyanotoxins achieved in 8 minutes; lowest limit of quantitation (LOQ) of 0.5 μg/L for most analytes (1.0 μg/L for MC-LF).
• Linearity and Precision: Calibration over 0.5–500 μg/L with R2 > 0.99; accuracy within 70–130 %; %RSD less than 15 % for calibration replicates.
• Spike Recovery: Water samples spiked at 8, 25, and 80 μg/L showed recoveries within ±20 % and precision below 10 % RSD; no carryover detected.
• Regulatory Comparison: LOQs more than ten times lower than those in EPA Method 544, enabling potential direct analysis without 500-fold preconcentration.

Benefits and Practical Applications

• Rapid 8-minute run time increases sample throughput for routine monitoring in drinking water utilities and environmental laboratories.
• High sensitivity and wide linear range support compliance with low μg/L regulatory limits.
• Avoidance of extensive sample preconcentration simplifies workflow and reduces analysis time and consumable costs.

Future Trends and Potential Applications

• Integration of on-line solid phase extraction to further enhance sensitivity and automation.
• Expansion of analyte panels to include emerging cyanotoxin variants and related compounds.
• Development of portable or field-deployable LC–MS platforms for real-time water monitoring.

Conclusion

The developed LC–MS/MS method using the Shimadzu LCMS-8060NX provides a rapid, sensitive, and reliable approach for quantifying multiple microcystins and nodularin in water. Its excellent linearity, low LOQs, and minimal sample preparation meet regulatory requirements and support routine environmental monitoring.

References

1. World Health Organization. Cyanobacterial toxins: microcystins. WHO/SDE/WSH/03.04/57.
2. U.S. Environmental Protection Agency. Method 544: Determination of microcystins and nodularin by LC–MS/MS.