Keywords: high resolution mass spectrometry Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 5-Methyl-Benzotriazole (LRUDIIUSNGCQKF-UHFFFAOYSA-N) 4-Hydroxy-Benzotriazole (NPZTUJOABDZTLV-UHFFFAOYSA-N) Acetochlor (VTNQPKFIQCLBDU-UHFFFAOYSA-N)