Determination of microcystins in cyanobacterial blooms by solid-phase microextraction-high-performance liquid chromatography

A solid-phase microextraction (SPME) method was applied to study microcystin (MC) profiles in a natural Microcystis sp. bloom in a freshwater pond in Guangzhou, China. Three dominant MC variants, namely MC-LR, MC-YR, and MC-RR, were quantified. Simultaneous study of their total, extracellular, and intracellular profiles was made possible using SPME coupled to high-performance liquid chromatography. The total and intracellular concentrations of MC-LR in the bloom were 8.67 × 10^-2 μg/ml and 1.93 mg/g, respectively. The corresponding concentrations of MC-YR were 1.20 × 10^-3 μg/ml and 0.06 mg/g, respectively, and those of MC-RR were 5.57 × 10^-2 μg/ml and 1.49 mg/g, respectively. Only MC-LR was detectable in the extracellular phase (1.49 × 10^-2 μg/ml) of the bloom, and its concentration was 14% of the intracellular content. Mass balance consideration revealed that only 71.1% of total MC-LR, 36.0% of total MC-YR, and 67.4% of total MC-RR within the cyanobacterial cells were released into the aqueous phase immediately after cell lysis.