Analytical method development for α-amanitin and β-amanitin in plasma at ultra-trace level by online solid phase extraction-high performance liquid chromatography-triple quadrupole mass spectrometry and its application in poisoning events

•An online SPE-LC–MS/MS analytical method for amanitins in plasma was developed.•The studied fatal mushroom toxins were α-amanitin and β-amanitin.•The method can analyze the toxins under ultra-trace level (0.02 ng mL-1) in plasma.•α-Amanitin was found to be a better indication for identification of the poisoning cause.•It’s applicable for the toxin confirmation in blood 40 h after poisoning.