Analysis of Microcystins in Drinking Water by LC/MS/MS and ELISA
Oral Presentation
Prepared by Y. Guo, M. Prescott, A. Lee
Metropolitan Water District of Southern California, 700 Moreno Avenue, La Verne, CA, 91750, United States
Contact Information: [email protected]; 909-392-7108
ABSTRACT
Cyanobacterial blooms have been reported worldwide with increasing frequency and intensity. Some cyanobacteria can produce cyanotoxins, many of which are detrimental to human health. Microcystins are the most prevalent type of cyanotoxins. The World Health Organization guideline for one microcystin variant (microcystin-LR [MCLR]) in finished drinking water is 1 µg/L. Microcystins are not volatile and cannot be analyzed by gas chromatography/mass spectrometry. This study evaluates two commonly used analytical methods for microcystins in water: liquid chromatography/tandem mass spectrometry (LC/MS/MS) and enzyme-linked immunosorbent assay (ELISA). Metropolitan’s current LC/MS/MS method quantitatively detects eight microcystin variants (MCLR, MCLA, MCYR, MCRR, MC-dmLR, MCLF, MCLW, and MCLY) using direct injection. The minimum reporting limit (MRL) for each analyte is 0.1 µg/L. Initial results showed varying degrees of matrix suppression for some microcystin variants (e.g., MCLR), depending on the sample matrices. ELISA is a semi-quantitative method based on antibody recognition, with a MRL of 0.15 µg/L for total microcystins (not individual variants). When samples containing MCLR were analyzed by both ELISA and LC/MS/MS methods, the results correlated very well. However, the ELISA results for another microcystin variant, MCLA, were biased high by 2-3 fold using MCLR as the calibration standards provided in commercial ELISA kits. ELISA results were improved when MCLA standards were used for calibration instead for samples containing MCLA. This suggests that appropriate variants are needed for calibration using ELISA method for more accurate results. Our study showed that, while ELISA is a rapid screening tool and detects a broader array of variants than LC/MS/MS, it can overestimate microcystin concentrations for certain variants. LC/MS/MS provides the specificity and sensitivity that may be needed to advise operational decisions. Better understanding and integration of the two methods is recommended for drinking water utilities to ensure effective cyanotoxin monitoring and management strategies.
Oral Presentation
Prepared by Y. Guo, M. Prescott, A. Lee
Metropolitan Water District of Southern California, 700 Moreno Avenue, La Verne, CA, 91750, United States
Contact Information: [email protected]; 909-392-7108
ABSTRACT
Cyanobacterial blooms have been reported worldwide with increasing frequency and intensity. Some cyanobacteria can produce cyanotoxins, many of which are detrimental to human health. Microcystins are the most prevalent type of cyanotoxins. The World Health Organization guideline for one microcystin variant (microcystin-LR [MCLR]) in finished drinking water is 1 µg/L. Microcystins are not volatile and cannot be analyzed by gas chromatography/mass spectrometry. This study evaluates two commonly used analytical methods for microcystins in water: liquid chromatography/tandem mass spectrometry (LC/MS/MS) and enzyme-linked immunosorbent assay (ELISA). Metropolitan’s current LC/MS/MS method quantitatively detects eight microcystin variants (MCLR, MCLA, MCYR, MCRR, MC-dmLR, MCLF, MCLW, and MCLY) using direct injection. The minimum reporting limit (MRL) for each analyte is 0.1 µg/L. Initial results showed varying degrees of matrix suppression for some microcystin variants (e.g., MCLR), depending on the sample matrices. ELISA is a semi-quantitative method based on antibody recognition, with a MRL of 0.15 µg/L for total microcystins (not individual variants). When samples containing MCLR were analyzed by both ELISA and LC/MS/MS methods, the results correlated very well. However, the ELISA results for another microcystin variant, MCLA, were biased high by 2-3 fold using MCLR as the calibration standards provided in commercial ELISA kits. ELISA results were improved when MCLA standards were used for calibration instead for samples containing MCLA. This suggests that appropriate variants are needed for calibration using ELISA method for more accurate results. Our study showed that, while ELISA is a rapid screening tool and detects a broader array of variants than LC/MS/MS, it can overestimate microcystin concentrations for certain variants. LC/MS/MS provides the specificity and sensitivity that may be needed to advise operational decisions. Better understanding and integration of the two methods is recommended for drinking water utilities to ensure effective cyanotoxin monitoring and management strategies.
