ISO/AWI 25616

Water quality — Determination of total microcystins in surface water by pre-oxidation and LC-MS/MS

Scope

This document specifies a method for the determination of total microcystins (MCs) in surface water by pre-oxidation to 3-methoxy-2-methyl-4-phenylbutyric acid (MMPB) followed by liquid chromatography–tandem mass spectrometry (LC-MS/MS).
The method is based on Lemieux-type oxidative cleavage of the ADDA side chain of microcystins to MMPB under controlled conditions providing sufficient and stable oxidation for both low and high concentrations of microcystins. After oxidation, the analyte is isolated by liquid or solid phase extraction and quantified by LC-MS/MS. Surrogate and internal standards can be used to assure traceability and reliability of the quantitative results.
This document is intended for the monitoring of cyanobacterial harmful algal blooms (HABs) and associated toxins in surface waters such as rivers, lakes and reservoirs used for drinking-water abstraction and recreational activities. It applies to raw waters before final disinfection.
This method is not intended for chlorinated or otherwise highly oxidized finished drinking waters, because microcystin chlorination by-products and other oxidation products can be converted to MMPB and lead to a positive bias in the measured “total microcystins” concentration. The applicability of this method to such matrices is therefore outside the scope of this document