Keywords: high resolution mass spectrometry Systems: groundwater Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 4-Hydroxy Diclofenac (KGVXVPRLBMWZLG-UHFFFAOYSA-N) 4-Dimethylaminoantipyrin (Aminopyrin) (RMMXTBMQSGEXHJ-UHFFFAOYSA-N)