Abstract :
[en] Cyanobacterial blooms are becoming more prevalent in western Europe due to eutrophication and increasing temperatures. To guarantee the safety of our drinking water and of recreational water activities, It is necessary to use adequate methods to detect hepatotoxic cyanotoxins. Thus, we adapted an LC-MS/MS method based on Turner et al (2018) to detect and quantify microcystin (MC) congeners and nodularin1. Additionally, we extended the method by providing an indication of the matrix effect (ME) for each sample without using a standard addition curve. Therefore, our analytical method is more compatible with monitoring programs that are needed to mitigate the risk for public health. These programs deal with a variety of matrix types with diverse physicochemical properties, of which water is the most important. Water can cause contamination through ingestion or MC accumulation in animals and plants. One of its variable physicochemical properties is the pH. While the Ohio EPA DES 701.0 method suggests a 5 to 11 pH range for their analysis of extracellular and intracellular toxins in different water sources2, EPA method 544 (LC-MS/MS) buffers the water samples at pH 7 during collection3. However, our validated method with simpler extraction (vs EPA 544) and LC-MS/MS detection method does not include buffering, resulting in a wide pH range during extraction (similar to Ohio EPA). This wide pH range can cause low extraction yield and recovery of some MC congeners and thus, in turn, imprecise total MC concentrations.
Consequently, we have assessed the impact of pH differences on the recovery of MC congeners using our validated LC-MS/MS method. We determined the recovery and ME of the MC’s in spiked samples of bottled spring water after adjusting the pH to different values between 5 and 11.
During the experiment, we found that the recovery of multiple congeners was influenced by a difference in pH. This prompted us to elaborate a uniform screening and quantification technique for all congeners.
References:
1. Turner et al. Development and single-laboratory validation of a UHPLC-MS/MS method for quantitation of microcystins and nodularin in natural water, cyanobacteria, shellfish and algal supplement tablet powders. J. Chromatogr. B Analyt. Technol. Biomed. Life. Sci. 1074–1075, 111–123 (2018).
2. Ohio EPA. Ohio EPA Total (Extracellular and Intracellular) Microcystins - ADDA by ELISA Analytical Methodology. Ohio EPA DES 701.0 Version 2.3, (2018).
3. Shoemaker et al. METHOD 544, v1 .0: DETERMINATION OF MICROCYSTINS AND NODULARIN IN DRINKING WATER BY SOLID PHASE EXTRACTION AND LIQUID CHROMATOGRAPHY/TANDEM MASS SPECTROMETRY (LC/MS/MS). EPA/600/R-14/474, (2015).
