Keywords: high resolution mass spectrometry Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 6-benzyladenine (NWBJYWHLCVSVIJ-UHFFFAOYSA-N) 1-(3-Trifluoromethylphenyl)-piperazine (KKIMDKMETPPURN-UHFFFAOYSA-N) 2-Aminobenzimidazole (JWYUFVNJZUSCSM-UHFFFAOYSA-N)