BS ISO 22104:2021 Water quality — Determination of microcystins — Method using liquid chromatography and tandem mass spectrometry (LC-MS/MS).
5.1 Biases
All labware that contacts microcystins should have relatively inert surfaces; otherwise, compound losses may occur by adsorption onto the glass. Unscratched horosilicate glassware or polyethylene is recommended. To further minimize this effect, sample preparation should be carried out in a timely manner and quantification by matrix matched calibration standards is preferred.
Analytical results (method precision and accuracy) are calculated by internal standard quantitation methods and may he affected by differences in the recovery of the internal standard relative to that of the target compounds. When available, 15N-lahelled microcystins should be used for this purpose.
The concentration of on-site samples will vary greatly depending on the density of algae at each sampling point, and the concentration difference will also be large for each microcystins. Given this, the multi-point calibration curves for the microcystins, using a fixed amount of internal standard, are nonlinear. Quantification is done by a second order (quadratic) curve-fitting procedure.
5.2 Limitations
The sample preparation method is restricted to water samples. Applicability of the method to samples with very high organic content, such as water containing high concentrations of hurnic materials, is unknown.
The working range of this method is 0,05 g/l to 1.6 g/l. If samples with a higher microcystin concentration than 1,5 jig/I are found or predicted, a smaller aliquot of sample should be taken, and a dilution factor applied to the final result. Surface waters containing thick cyanobacterial blooms may interfere with the instrumental analysis. In these cases, a smaller amount of sample can be diluted, and volume should be recorded for the final calculation of microcystins concentration.
Standards of specific microcystin variants are not always available on a continuous basis. Foreign suppliers are sometimes restricted by law and are not always able to export algal toxin standards to different countries. Before being used, newly prepared standards shall be compared to standards in current use. Purity of the different lots of standards should be checked against reference materials when available. Alternatively, purity can also be confirmed using universal detector like HPLC-UV
(ISO 20179).
6 Reagents and standards
6.1 General
If available, reagents of purity grade “for analysis” or “for residue analysis” are used. The amount of impurities contributing to the blank value or causing signal interferences shall be negligible. This shall be checked regularly (see section for blank value measurements).
Solvent, water and reagents intended for use as elution agents shall be compatible with HPLC and mass spectrometry.BS ISO 22104 pdf download.