Determination of Five Microcystins in Cyanobacteria by Liquid Chromatography Tandem Mass Spectrometry Using Freezing-thawing and Solid Phase Extraction
A method was developed for simultaneous determination of five microcystins( MCs) in Cyanobacteria by liquid chromatography Tandem mass spectrometry( LC-MS/MS) using freezing-thawing and solid phase extraction( SPE).Cyanobacteria in environmental water was collected by 0.45 μm hybrid filter and extracted with two times of 5 mL 75% methanol after three times of-20 ℃/37 ℃ freezing-thawing.The extract was concentrated by end-capped C18SPE cartridge with a clean-up by 10 mL 5% methanol.Five MCs were detected by LC-MS/MS with multiple reaction monitoring and external standard method.Gradient elution was employed with a mobile phase consisting of acetonitrile with 0.1% formic acid and water with 0.1%formic acid on C18column( 50 mm×2.1 mm,1.7 μm).The method showed good linear correlations in a range of 1.25-50 μg/L with correlation coefficients greater than 0.995.RSD and LOD were 3.0%-11.5%and 0.05-0.2 ng,respectively.Recovery of three spiked levels( 1,5 and 50 ng) for five MCs were63.7%-100.4%( RSD 5.5%-13.1%),72.6%-85.7%( RSD 3.1%-6.6%) and 72.5%-80.5%( RSD 2.6%-8.3%),respectively.The proposed method was applied in the detection of intracellular and extracellular MCs in one drinking water source of South China from August to December.