A validated method for quantitation of psilocin in plasma by LC-MS/MS and study of stability

A liquid chromatography-electrospray ionization/tandem mass spectrometry method for the quantitation of psilocin in plasma is presented. Sample workup was performed with mixed-mode solid-phase extraction using ascorbic acid and nitrogen for drying to protect the unstable analyte. Calibration curves were linear from 2 to 100 ng/mL, and no selectivity problems occurred. The limit of detection was 0.1 ng/mL, and the limit of quantitation was 0.34 ng/mL. Recovery was > 86% and matrix effects were < 110%. Both were reproducible. Interday and intraday precisions at different concentrations were 1.5-4.3% relative standard deviation, bias within +/- 9%. Processed samples were stable in the autosampler for at least 26 h. Furthermore, the stability of psilocin in blood stored at different temperatures over various periods of time was investigated. Samples stored at room temperature showed a continuous decrease of analyte leading to a loss of about 90% after 1 week. Storage in the fridge improved sample stability significantly. Freezing of blood samples led to a not reproducible loss of psilocin.