The extraction and stability of microcystin-RR in different solvents

Abstract

Samples of a hepatotoxic strain of the cyanobacterium Microcystis aeruginosa (Kützing) Lemmennann CYA 228/1 were collected on 47-mm GF/C filters. The moist filters were frozen and thawed. After thawing, the filters were extracted with water, 5% acetic acid, 70% methanol or 100% methanol. After extraction and determination of the toxin content, the extracts were stored for 32 days at 4°C in the dark, and the toxin content in the different extracts was measured at regular intervals during this period. It was found that all the solvents extracted microcystin RR with the same efficiency, and a second extraction with the same or another solvent did not contain detectable toxin. During storage. microcystin-RR degraded rapidly in 5% acetic acid, whereas no degradation was found after c. 3 weeks in the other solvents. After c. 3 weeks, the toxin in the water extracts also degraded rapidly, whereas the toxin in the methanol extracts was stable during the entire period.