Keywords: high resolution mass spectrometry Systems: groundwater Substances: 4-Formylaminoantipyrin (4-FAA) (WSJBSKRPKADYRQ-UHFFFAOYSA-N) 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 2-4-dimethylphenylformamide (JOFDPSBOUCXJCC-UHFFFAOYSA-N)