Assessment of [18F]fluoroethylflumazenil metabolites using high-performance liquid chromatography and tandem mass spectrometry

A simple procedure using HPLC and tandem mass spectrometry has been developed for the determination of fluoroethylflumazenil metabolites. Samples were precipitated with acetonitrile, evaporated to dryness followed by reconstitution with methanol. As mobile phase, 50 mM ammonium formate–methanol (58:42, v/v) was used. The method is valid both for cold and radiolabelled metabolites. Various cold metabolites (hydroxylated and/or dealkylated) were identified in rat and human microsome preparations. Radiolabelled metabolites arise from two or more transformations including hydroxylation. The methodology developed can be applied for further characterisation of metabolites, and for the determination of non metabolised [18F]fluoroethylflumazenil in routine clinical analysis.