Method Development and Validation for Simultaneous Quantification of Microcystin Congeners in Water

Microcystins (MCs) are secondary metabolites of cyanobacteria that are hepatotoxic to humans through the ingestion of cyanobacteria-contaminated water and accidental inhalation from lake activities. MCs with diverse congeners in water can be precisely quantified using online solid-phase extraction-ultra performance liquid chromatography coupled with tandem mass spectrometry (online-SPE UPLC–MS/MS). A method was developed and validated to simultaneously quantify eight different MCs (microcystin-RR, -LR, -YR, -WR, -LA, -LF, -LY, and -LW) in water using online-SPE UPLC–MS/MS. The method achieved the highest efficiency and sensitivity by selecting acetonitrile with 0.1% formic acid and water with 0.1% formic acid as the best mobile phase conditions. The linearity, accuracy, and precision were validated using matrix-mixed water with a leucine enkephalin internal standard. The limit of detection (LOD) was calculated using the signal-to-noise ratio of three passes of the daily water-surface inspection for MCs. This method showed both high sensitivity and high resolution for the separation of eight MC congeners with LODs ranging from 0.020 to 0.371 ng L–1 and limits of quantitation ranging from 0.066 to 1.24 ng L–1. The detection time was reduced to 11 min. Except for MC-RR (58.8% recovery at high concentration) and MC-WR (45.1% and 40.9% recoveries at medium and high concentrations, respectively), the recoveries of the other MCs ranged from 70 to 135%, and the relative standard deviation was less than 10%. Eight different MCs in 12 water samples collected from Chaohu Lake, China, were analyzed. The sum of all MC congeners was calculated to range from 101 to 585 ng L–1 (less than the World Health Organization’s safe drinking water limit of 1 μg L–1 for MC-LR).