BS ISO 22104:2021 pdf download – 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 borosilicate 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 be affected by differences in the recovery of the internal standard relative to that of the target compounds. When available, 15 N-labelled 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 non- linear. 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 humic materials, is unknown. The working range of this method is 0,05 µg/l to 1,6 µg/l. If samples with a higher microcystin concentration than 1,5 µg/l 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. Microcystins are potent hepatotoxins. Laboratory safety measures should be strictly followed throughout the sample preparation (including lab gloves, labcoat, safety glasses) to prevent human exposure to these toxins.
NOTE 1 High purity grades of solvent applicable for use are available commercially.
NOTE 2 Reagents listed as “prepare as required” have an expiry date of one year from the moment they were prepared. NOTE 3 Prepared standard solutions are stored at (5 ± 3) °C, with an expiry date of one year from the moment they were prepared. Stock and intermediate standard solutions should be used as a reference, other stock and intermediate concentrations are acceptable to prepare the final working solutions.
6.2 Preparation of solutions
6.2.1 Tap water, quenched with sodium thiosulfate at 150 mg/l (for calibration standard solutions, QC samples and sample dilutions). The method blank, calibration standard solutions, QC samples and sample dilutions (if necessary) are made with quenched laboratory tap water. This quenched water is made by taking 1 l of tap water and adding 1,5 ml of sodium thiosulfate preservative solution (i.e. 150 mg sodium thiosulfate) (6.2.2). Cap the bottle and shake vigorously to mix. This water is prepared as required before sample preparation in order to quench any residual chlorine in the tap water which would oxidize the microcystins. Store the reagent water at room temperature. Quenching is not necessary if it can be ensured that the used tap water is provided without chlorination.BS ISO 22104 pdf download.