Accurate LC-MS analyses for microcystins using per-15N-labeled microcystins

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Microbiology

Background:

• Microcystins are potent cyanobacterial toxins posing risks to aquatic ecosystems and human health.
• Accurate quantification of microcystins is crucial for risk assessment and environmental monitoring.
• Existing analytical methods may face challenges in precise microcystin quantification.

Purpose of the Study:

• To develop and validate per-(15)N-labeled microcystins as internal standards for accurate quantification.
• To assess the efficacy of these labeled compounds in liquid chromatography-mass spectrometry (LC-MS) analysis.
• To confirm the structural integrity and suitability of labeled microcystins as surrogates.

Main Methods:

• Culturing two strains of Microcystis aeruginosa in (15)NO(3)-containing medium for over six months to achieve complete nitrogen isotope incorporation.
• Extraction and purification of per-(15)N-labeled microcystin variants using high-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC).
• Structural confirmation of labeled microcystins via mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy.

Main Results:

• Successfully prepared per-(15)N-labeled microcystin variants from cultured Microcystis aeruginosa.
• Demonstrated complete separation of mass-to-charge (m/z) signals between native and labeled microcystins during LC-MS analysis.
• Achieved excellent quantitative accuracy (98-106%) when using per-(15)N-labeled microcystins as surrogates.

Conclusions:

• Per-(15)N-labeled microcystins are highly effective surrogates for accurate microcystin quantification.
• The developed method using labeled microcystins significantly enhances the reliability of LC-MS analysis for toxin detection.
• This approach provides a robust tool for environmental monitoring and toxicological studies of cyanobacterial blooms.