Variables: concentration Keywords: high resolution mass spectrometry Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 4-Aminopyrin (4-Aminoantipyrin 4-AA) (RLFWWDJHLFCNIJ-UHFFFAOYSA-N) 4-Hydroxy-Benzotriazole (NPZTUJOABDZTLV-UHFFFAOYSA-N)